Spectroscopic Detection of Cyano-Cyclopentadiene Ions as Dissociation Products upon Ionization of AnilineClick to copy article linkArticle link copied!
- Daniël B. RapDaniël B. RapRadboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The NetherlandsMore by Daniël B. Rap
- Tom J. H. H. van BoxtelTom J. H. H. van BoxtelRadboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The NetherlandsMore by Tom J. H. H. van Boxtel
- Britta RedlichBritta RedlichRadboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The NetherlandsMore by Britta Redlich
- Sandra Brünken*Sandra Brünken*Email: [email protected]Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The NetherlandsMore by Sandra Brünken
Abstract
The H-loss products (C6H6N+) from the dissociative ionization of aniline (C6H7N) have been studied by infrared predissociation spectroscopy in a cryogenic ion trap instrument at the free electron laser for infrared experiments (FELIX) laboratory. Broadband and narrow line width vibrational spectra in the spectral fingerprint region of 550–1800 cm–1 have been recorded. The comparison to calculated spectra of the potential isomeric structures of the fragment ions reveals that the dominant fragments are five-membered cyano-cyclopentadiene ions. Computed C6H7N•+ potential energy surfaces suggest that the dissociation path leading to H loss starts with an isomerization process, following a similar trajectory as the one leading to HNC loss. The possible presence of cyano-cyclopentadiene ions and related five-membered ring species in Titan’s atmosphere and the interstellar medium are discussed.
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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Special Issue
Published as part of The Journal of Physical Chemistry virtual special issue “10 Years of the ACS PHYS Astrochemistry Subdivision”.
Introduction
Experimental and Computational Methods
FELion Cryogenic 22-Pole Ion Trap Instrument at the FELIX Laboratory

Quantum Chemical Calculations
Results and Discussion
Fragmentation Mass Spectrometry
Figure 1
Figure 1. Experimental mass spectra showing the ionization and fragmentation of aniline in (a) the storage ion source at 40 eV and (b) the direct electron impact source at electron energies of 20 eV (33) (black) and 50 eV (pink). The most important fragmentation channels C6H6N+ (m/z 92, H loss), C5H6•+ (m/z 66, HNC loss), and C5H5+ or C4H3N•+ (m/z 65, HNCH or C2H4 loss) are labeled.
Infrared Fingerprinting
Figure 2
Figure 2. Experimental infrared predissociation spectrum of C6H6N+–Ne (gray) and calculated anharmonic infrared spectra of H-1-cyano-CPD+ (pink) and H-2-cyano-CPD+ (blue) plotted with sticks. The inset shows a close-up of the lower wavenumber region. The B3LYP-GD3/N07D level of theory was used to optimize the geometries of the two isomers and calculate the vibrational frequencies.
Figure 3
Figure 3. Overview of the different fragmentation pathways of aniline•+ via (pathway 1) direct H loss, (pathway 3) isomerization and HNC loss, and (pathways 2 and 4) isomerization and H loss. The potential energy surface was evaluated using the CBS-QB3 method. The zero-point corrected electronic energies are given relative to aniline•+ (1) in kJ/mol between parentheses for minima and above the arrows for transitions states, respectively. The structures observed here are colored in pink and blue according to the structures 11 and 12 from Figure 2, respectively.
Figure 4
Figure 4. Experimental infrared spectrum of m/z 92 (gray) and comparison with the calculated anharmonic frequencies of (a) anilino+ (red), (b) 1-dehydro-aniline+ (green), (c) azatropylium+ (blue), and (d) H-5-cyano-CPD+ (brown).
Potential Energy Surface of Fragmentation
Astrophysical Implications and Conclusions
H-1-cyano-CPD+ | 1-cyano-CPD | 1-cyano-CPD | |
---|---|---|---|
molecular constants | calc | exp | calc |
A (MHz) | 8168.9 | 8352.981(10) | 8345.8 |
B (MHz) | 1839.9 | 1904.2522(2) | 1896.4 |
C (MHz) | 1517.6 | 1565.3652(2) | 1560.2 |
μa,b,c (Debye) | 2.7/0.2/0.8 | 4.6/0.3/0 |
H-2-cyano-CPD+ | 2-cyano-CPD | 2-cyano-CPD | |
---|---|---|---|
molecular constants | calc | exp | calc |
A (MHz) | 8097.1 | 8235.592(14) | 8219.3 |
B (MHz) | 1835.2 | 1902.0748(3) | 1895.5 |
C (MHz) | 1509.9 | 1559.6472(2) | 1555.1 |
μa,b,c (Debye) | 4.2/1.1/0 | 5.0/0.6/0 |
H-5-cyano-CPD+ | 5-cyano-CPD | |
---|---|---|
molecular constants | calc | calc |
A (MHz) | 6208.4 | 6742.9 |
B (MHz) | 2111.5 | 2091.7 |
C (MHz) | 1798.9 | 1755.3 |
μa,b,c (Debye) | 4.9/0/0.5 | 3.9/0/1.5 |
The experimental rotational constants have been taken from Kelvin Lee et al. (9) The rotational constants have been calculated at the B3LYP-GD3/N07D level of theory.
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpca.2c01429.
Mass spectrum of m/z 92 Ne tagging; saturation depletion scans (PDF)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Acknowledgments
We gratefully acknowledge the support of Radboud University and of the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) for providing the required beam time at the FELIX laboratory and the skillful assistance of the FELIX staff. This work was sponsored by NWO Exact and Natural Sciences for the use of supercomputer facilities at SURFsara in Amsterdam (NWO Rekentijd grant 2021.055). We thank the Cologne Laboratory Astrophysics group for providing the FELion ion trap instrument for the current experiments and the Cologne Center for Terahertz Spectroscopy funded by the Deutsche Forschungsgemeinschaft (DFG, grant SCHL 341/15-1) for supporting its operation. We thank Jos Oomens for helpful discussions.
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- 17Vuitton, V.; Yelle, R. V.; McEwan, M. J. Ion Chemistry and N-Containing Molecules in Titan’s Upper Atmosphere. Icarus 2007, 191 (2), 722– 742, DOI: 10.1016/j.icarus.2007.06.023Google ScholarThere is no corresponding record for this reference.
- 18Anicich, V. G.; McEwan, M. J. Ion–Molecule Chemistry in Titan’s Ionosphere. Planet. Space Sci. 1997, 45 (8), 897– 921, DOI: 10.1016/S0032-0633(97)00053-6Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXmvFGgtbc%253D&md5=2dd5d04636c3f39ded03adb4502e1d34Ion-molecule chemistry in Titan's ionosphereAnicich, Vincent G.; Mcewan, Murray J.Planetary and Space Science (1997), 45 (8), 897-921CODEN: PLSSAE; ISSN:0032-0633. (Elsevier)A review with many refs. A summary is presented of the information available from lab. studies of ion-mol. reactions that is relevant to the chem. occurring in Titan's ionosphere. Reaction information from the literature has been collated and many new reactions have been measured, including some ion-atom reactions. The sequences of ion-neutral reactions can lead to a rapid increase in ion size. How this increase may lead to aerosol prodn. at the base of the ionosphere is briefly discussed. Lab. observations of extremely rapid termol. ion-neutral assocn. reactions indicate that these assocn. reactions are viable contributors to the ion chem. at the base of Titan's ionosphere.
- 19West, B.; Joblin, C.; Blanchet, V.; Bodi, A.; Sztáray, B.; Mayer, P. M. On the Dissociation of the Naphthalene Radical Cation: New IPEPICO and Tandem Mass Spectrometry Results. J. Phys. Chem. A 2012, 116 (45), 10999– 11007, DOI: 10.1021/jp3091705Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFClsLvE&md5=8b773c4bb6a4ac2b550d775730dae5eaOn the Dissociation of the Naphthalene Radical Cation: New iPEPICO and Tandem Mass Spectrometry ResultsWest, Brandi; Joblin, Christine; Blanchet, Valerie; Bodi, Andras; Sztaray, Balint; Mayer, Paul M.Journal of Physical Chemistry A (2012), 116 (45), 10999-11007CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)The dissocn. of the naphthalene radical cation was restudied here by a combination of tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C10H8•+ → C10H7+ + H (m/z = 127); (R2) C10H8•+ → C8H6•+ + C2H2 (m/z = 102); (R3) C10H8•+ → C6H6•+ + C4H2 (m/z = 78); (R4) C10H8•+ → C10H6•+ + H2 (m/z = 126); (R5) C10H7+ → C6H5+ + C4H2 (m/z = 77); (R6) C10H7+ → C10H6•+ + H (m/z = 126). The E0 activation energies for the reactions deduced from the present measurements are (in eV) 4.20 ± 0.04 (R1), 4.12 ± 0.05 (R2), 4.27 ± 0.07 (R3), 4.72 ± 0.06 (R4), 3.69 ± 0.26 (R5), and 3.20 ± 0.13 (R6). The corresponding entropies of activation, ΔS‡1000K, derived in the present study are (in J K-1 mol-1) 2 ± 2 (R1), 0 ± 2 (R2), 4 ± 4 (R3), 11 ± 4 (R4), 5 ± 15 (R5), and -19 ± 11 (R6). The derived E0 value, combined with the previously reported IE of naphthalene (8.1442 eV) results in an enthalpy of formation for the naphthyl cation, ΔfH°0K = 1148 ± 14 kJ mol-1/ΔfH°298K = 1123 ± 14 kJ mol-1 (site of dehydrogenation unspecified), slightly lower than the previous est. by Gotkis and co-workers. The derived E0 for the second H-loss leads to a ΔfH° for ion 7, the cycloprop[a]indene radical cation, of ΔfH°0K =1457 ± 27 kJ mol-1/ΔfH°298K(C10H6+) = 1432 ± 27 kJ mol-1. Detailed comparisons are provided with values (exptl. and theor.) available in the literature.
- 20Bouwman, J.; De Haas, A. J.; Oomens, J. Spectroscopic Evidence for the Formation of Pentalene+ in the Dissociative Ionization of Naphthalene. Chem. Commun. 2016, 52 (12), 2636– 2638, DOI: 10.1039/C5CC10090AGoogle Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjslemtQ%253D%253D&md5=358f1d8954f78741f1ec61c6dcb45a48Spectroscopic evidence for the formation of pentalene+ in the dissociative ionization of naphthaleneBouwman, Jordy; de Haas, Arjen J.; Oomens, JosChemical Communications (Cambridge, United Kingdom) (2016), 52 (12), 2636-2638CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Although acetylene loss is well known to constitute the main breakdown pathway of polycyclic arom. hydrocarbon (PAH) species, the mol. structure of the dissocn. products remains only poorly characterized. For instance, the structure of the C8H6 product ion formed upon acetylene loss from the smallest PAH naphthalene (C10H8) has not been exptl. established. Several C8H6+ isomers are conceivable, including phenylacetylene, benzocyclobutadiene, pentalene as well as a no. of acyclic products. Here we present IR spectroscopic evidence for the formation of the (anti-arom.) pentalene structure using a combination of tandem mass spectrometry and IR laser spectroscopy. The formation of pentalene is suggestive of facile 6- to 5-membered ring conversion, which possibly has implications for the PAH/fullerene interrelationship in energetic settings such as the interstellar medium and combustion environments.
- 21Panchagnula, S.; Bouwman, J.; Rap, D. B.; Castellanos, P.; Candian, A.; Mackie, C.; Banhatti, S.; Brünken, S.; Linnartz, H.; Tielens, A. G. G. M. Structural Investigation of Doubly-Dehydrogenated Pyrene Cations. Phys. Chem. Chem. Phys. 2020, 22, 21651, DOI: 10.1039/D0CP02272AGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB38jovFalsw%253D%253D&md5=8188f13b115a70796f9cc0fdd8308c72Structural investigation of doubly-dehydrogenated pyrene cationsPanchagnula Sanjana; Bouwman Jordy; Rap Daniel B; Castellanos Pablo; Candian Alessandra; Mackie Cameron; Banhatti Shreyak; Brunken Sandra; Linnartz Harold; Tielens Alexander G G MPhysical chemistry chemical physics : PCCP (2020), 22 (38), 21651-21663 ISSN:.The vibrationally resolved spectra of the pyrene cation and doubly-dehydrogenated pyrene cation (C16H10(+); Py(+) and C16H8(+); ddPy(+)) are presented. Infrared predissociation spectroscopy is employed to measure the vibrational spectrum of both species using a cryogenically cooled 22-pole ion trap. The spectrum of Py(+) allows a detailed comparison with harmonic and anharmonic density functional theory (DFT) calculated normal mode frequencies. The spectrum of ddPy(+) is dominated by absorption features from two isomers (4,5-ddPy(+) and 1,2-ddPy(+)) with, at most, minor contributions from other isomers. These findings can be extended to explore the release of hydrogen from interstellar PAH species. Our results suggest that this process favours the loss of adjacent hydrogen atoms.
- 22Lemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Willemsen, B.; Rijs, A. M. Polycyclic Aromatic Hydrocarbon Formation Chemistry in a Plasma Jet Revealed by IR-UV Action Spectroscopy. Nat. Commun. 2020, 11 (1), 269, DOI: 10.1038/s41467-019-14092-3Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXivFOgsbY%253D&md5=80b9778670e41e77740d8533b9a98168Polycyclic aromatic hydrocarbon formation chemistry in a plasma jet revealed by IR-UV action spectroscopyLemmens, Alexander K.; Rap, Daniel B.; Thunnissen, Johannes M. M.; Willemsen, Bryan; Rijs, Anouk M.Nature Communications (2020), 11 (1), 269CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Large polycyclic arom. hydrocarbons (PAHs) are the most abundant complex mols. in the interstellar medium; however, their possible formation pathways from small mol. species are still elusive. In the present work, we follow and characterize the formation of PAHs in an elec. discharge, specifically the PAH naphthalene in a mol. beam of argon. The fragments, products and reaction intermediates are unambiguously structurally identified by mass-selective IR-UV spectroscopy combined with quantum chem. calcns. This expt. provides evidence of the formation of larger PAHs contg. up to four cyclic rings in the gas phase originating from a non-radical PAH mol. as a precursor. In addn. to PAH formation, key resonance stabilized radical intermediates and intermediates contg. di-acetylenic side groups are unambiguously identified in our expt. We thereby not only reveal competing formation pathways to larger PAHs, but also identify intermediate species to PAH formation that are candidates for detection in radio-astronomy.
- 23Lee, K. L. K.; McCarthy, M. Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave Spectroscopy. J. Phys. Chem. Lett. 2019, 10 (10), 2408– 2413, DOI: 10.1021/acs.jpclett.9b00586Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXot1yjsbk%253D&md5=f020b3e9ee45e5b17f2be2cf52e2e3c7Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave SpectroscopyLee, Kin Long Kelvin; McCarthy, MichaelJournal of Physical Chemistry Letters (2019), 10 (10), 2408-2413CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Using a combination of broadband and cavity Fourier transform microwave spectroscopies, and newly developed anal. and assignment tools, the discharge products of benzene have been extensively studied in the 2-18 GHz frequency range. More than 450 spectral features with intensities greater than 6σ of the noise RMS were identified, of which of roughly four-fifths (82%) constituting 90% of the total spectral intensity were assigned to 38 species previously detected in the radio band, and nine entirely new hydrocarbon mols. were identified. The new species include both branched and chain fragments of benzene, high energy C6H6 isomers, and larger mols. such as phenyldiacetylene and isomers of fulvenallene; taken together they account for roughly half of the no. of obsd. transitions and 51% of the spectral line intensity. Transitions from vibrationally excited states of several mols. were also identified in the course of this investigation. A key aspect of the present anal. was implementation of a rapid and efficient workflow to assign spectral features from known mols. and to identify line progressions by pattern recognition techniques.
- 24McCarthy, M. C.; Lee, K. L. K.; Carroll, P. B.; Porterfield, J. P.; Changala, P. B.; Thorpe, J. H.; Stanton, J. F. Exhaustive Product Analysis of Three Benzene Discharges by Microwave Spectroscopy. J. Phys. Chem. A 2020, 124 (25), 5170– 5181, DOI: 10.1021/acs.jpca.0c02919Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXpvVGqsL8%253D&md5=e97b9dbf3992cbc51a9dc6406154c5cbExhaustive Product Analysis of Three Benzene Discharges by Microwave SpectroscopyMcCarthy, Michael C.; Lee, Kin Long Kelvin; Carroll, P. Brandon; Porterfield, Jessica P.; Changala, P. Bryan; Thorpe, James H.; Stanton, John F.Journal of Physical Chemistry A (2020), 124 (25), 5170-5181CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)Using chirped and cavity microwave spectroscopies, automated double resonance, new high-speed fitting and deep learning algorithms, and large databases of computed structures, the discharge products of benzene alone, or in combination with mol. oxygen or nitrogen, have been exhaustively characterized between 6.5 and 26 GHz. In total, more than 3300 spectral features were obsd.; 89% of these, accounting for 97% of the total intensity, have now been assigned to 152 distinct chem. species and 60 of their variants (i.e., isotopic species and vibrationally excited states). Roughly 50 of the products are entirely new or poorly characterized at high resoln., including many heavier by mass than the precursor benzene. These findings provide direct evidence for a rich architecture of two- and three-dimensional carbon and indicate that benzene growth, particularly the formation of ring-chain mols., occurs facilely under our exptl. conditions. The present anal. also illustrates the utility of microwave spectroscopy as a precision tool for complex mixt. anal., irresp. of whether the rotational spectrum of a product species is known a priori or not. From this large quantity of data, for example, it is possible to det. with confidence the relative abundances of different product masses, but more importantly the relative abundances of different isomers with the same mass. The complementary nature of this type of anal. to traditional mass spectrometry is discussed.
- 25Roberts, G. M.; Williams, C. A.; Young, J. D.; Ullrich, S.; Paterson, M. J.; Stavros, V. G. Unraveling Ultrafast Dynamics in Photoexcited Aniline. J. Am. Chem. Soc. 2012, 134 (30), 12578– 12589, DOI: 10.1021/ja3029729Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XovFaks7o%253D&md5=62d18b1b7a3caeb954ab9956e320a449Unraveling Ultrafast Dynamics in Photoexcited AnilineRoberts, Gareth M.; Williams, Craig A.; Young, Jamie D.; Ullrich, Susanne; Paterson, Martin J.; Stavros, Vasilios G.Journal of the American Chemical Society (2012), 134 (30), 12578-12589CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A combination of ultrafast time-resolved velocity map imaging (TR-VMI) methods and complete active space SCF (CASSCF) ab initio calcns. are implemented to investigate the electronic excited-state dynamics in aniline (aminobenzene), with a perspective for simulation, physicochem., physicochem. 1πσ* mediated dynamics along the amino moiety in the purine derived DNA bases. This synergy between expt. and theory has enabled a comprehensive picture of the photochem. pathways/conical intersections (CIs), which govern the dynamics in aniline, to be established over a wide range of excitation wavelengths. TR-VMI studies following excitation to the lowest-lying 1ππ* state (11ππ*) with a broadband femtosecond laser radiation pulse, centered at wavelengths longer than 250 nm (4.97 eV), do not generate any measurable signature for 1πσ* driven N-H bond fission on the amino group. Between wavelengths of 250 and >240 nm (<5.17 eV), coupling from 11ππ* onto the 1πσ* state at a 11ππ*/1πσ* CI facilitates ultrafast nonadiabatic N-H bond fission through a 1πσ*/S0 CI in <1 silicon::polycryst.,, a notion supported by CASSCF results. For excitation to the higher lying 21ππ* state, calcns. reveal a near barrierless pathway for CI coupling between the 21ππ* and 11ππ* states, enabling the excited-state population to evolve through a rapid sequential 21ππ* → 11ππ* → 1πσ* → N-H fission mechanism, which we observe to take place in 155 ± 30 fs at 240 nm. We also postulate that an analogous cascade of CI couplings facilitates N-H bond scission along the 1πσ* state in 170 ± 20 fs, following 200 nm (6.21 eV) excitation to the 31ππ* surface. Particularly illuminating is the fact that a no. of the CASSCF calcd. CI geometries in aniline bear an exceptional resemblance with previously calcd. CIs and potential energy profiles along the amino moiety in guanine, strongly suggesting that the results here may act as an excellent grounding for better understanding 1πσ* driven dynamics in this ubiquitous genetic building block.
- 26King, G. A.; Oliver, T. A. A.; Ashfold, M. N. R. Dynamical Insights into π1σ* State Mediated Photodissociation of Aniline. J. Chem. Phys. 2010, 132 (21), 214307, DOI: 10.1063/1.3427544Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXntVSrsrg%253D&md5=02fe7132c96e50f63ba5e2ccc8fb8270Dynamical insights into 1πσ* state mediated photodissociation of anilineKing, Graeme A.; Oliver, Thomas A. A.; Ashfold, Michael N. R.Journal of Chemical Physics (2010), 132 (21), 214307/1-214307/12CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)This article reports a comprehensive study of the mechanisms of H atom loss in aniline (C6H5NH2) following UV excitation, using H (Rydberg) atom photofragment translational spectroscopy. N-H bond fission via the low lying 1πσ* electronic state of aniline is exptl. demonstrated. The 1πσ* potential energy surface (PES) of this prototypical arom. amine is essentially repulsive along the N-H stretch coordinate, but possesses a shallow potential well in the vertical Franck-Condon region, supporting quasibound vibrational levels. Photoexcitation at wavelengths (λphot) in the range 293.859 nm ≥ λphot ≥ 193.3 nm yields H atom loss via a range of mechanisms. With λphot resonant with the 11ππ*←S0 origin (293.859 nm), H atom loss proceeds via, predominantly, multiphoton excitation processes, resonantly enhanced at the one photon energy by the first 1ππ* excited state (the 11ππ* state). Direct excitation to the first few quasibound vibrational levels of the 1πσ* state (at wavelengths in the range 269.513 nm ≥ λphot ≥ 260 nm) induces N-H bond fission via H atom tunneling through an exit barrier into the repulsive region of the 1πσ* PES, forming anilino (C6H5NH) radical products in their ground electronic state, and with very limited vibrational excitation; the photo-prepd. vibrational mode in the 1πσ* state generally evolves adiabatically into the corresponding mode of the anilino radical upon dissocn. However, as the excitation wavelength is reduced (λphot < 260 nm), N-H bond fission yields fragments with substantially greater vibrational excitation, rationalized in terms of direct excitation to 11ππ* levels, followed by coupling to the 1πσ* PES via a 11ππ*/1πσ* conical intersection. Changes in product kinetic energy disposal once λphot approaches ∼ 230 nm likely indicate that the photodissocn. pathways of aniline proceed via direct excitation to the (higher) 21ππ* state. Anal. of the anilino fragment vibrational energy disposal-and thus the concomitant dynamics of 1πσ* state mediated photodissocn.-provides a particularly interesting study of competing σ*←π and π*←π absorption processes and develops our appreciation of the photochem. of arom. amines. It also allows revealing comparisons with simple amines (such as ammonia and methylamine) as well as the isoelectronic species, phenol. This study yields a value for the N-H bond strength in aniline, D0(H-anilino) = 31630 ± 40 cm-1. (c) 2010 American Institute of Physics.
- 27Roohi, H.; Moghadam, B. Decomposition Mechanism of the Phenylaminyl C6H5NH Radical to Propargyl and Acetylene: A M06-2X, CBS-QB3 and G4 Study. Chem. Phys. Lett. 2019, 730, 332– 339, DOI: 10.1016/j.cplett.2019.06.018Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFyit7zP&md5=228cc69ac4862667a15aec1bbd25b205Decomposition mechanism of the phenylaminyl C6H5N·H radical to propargyl and acetylene: A M06-2X, CBS-QB3 and G4 studyRoohi, Hossein; Moghadam, BehnazChemical Physics Letters (2019), 730 (), 332-339CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)In this work, decompn. mechanism of the phenylaminyl radical C6H5N·H was investigated by means of M062X, G4 and CBS-QB3 methods. It is found that the energy barrier for conversion of most stable N-centered radical to less stable C-centered radicals is greater than the decompn. reaction. Two resonantly stabilized radicals propargyl and cyclopentadienyl were found on the potential energy surface of reaction. It is estd. that activation energy for sigmatropic H transfer rearrangement of cyclopentadienyl radical is 59.50 and 56.26 kcal/mol at G4 and M06-2X/6-311++G(d,p) levels, resp. The ΔH°f,g and ΔG°f,g values of all the radicals were calcd.
- 28Kühlewind, H.; Neusser, H. J.; Schlag, E. W. Multiphoton Metastable Ion Spectra and Ion Dissociation Kinetics: Analysis of the Decay Channels of the Aniline Cation with a Reflectron Time-of-Flight Instrument. J. Chem. Phys. 1985, 82 (12), 5452– 5456, DOI: 10.1063/1.448579Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlslOrsLw%253D&md5=ecc0790fec73c7cad28b66de0e7ae4c3Multiphoton metastable ion spectra and ion dissociation kinetics: analysis of the decay channels of the aniline cation with a reflectron time-of-flight instrumentKuehlewind, H.; Neusser, H. J.; Schlag, E. W.Journal of Chemical Physics (1985), 82 (12), 5452-6CODEN: JCPSA6; ISSN:0021-9606.Multiphoton mass spectrometry when carried out in conjunction with a reflecting field time-of-flight mass spectrometer yields rich new metastable ion spectra of polyat. mols., here aniline. The reflecting field acting also as an energy analyzer is particularly suitable for sensitive metastable ion detection without interference from stable fragment ions. With this technique several new metastable ion decay channels of the aniline cation have been obsd. On the basis of the measured metastable ion spectrum a reasonable fragmentation pathway for the aniline cation C6H7N+ after multiphoton excitation is presented. The prominent intensity of the metastable ion peak C5H6+ points to a narrow energy distribution within the aniline cation typical for a ladder switching multiphoton excitation mechanism.
- 29Geng, L.; Zhang, H.; Wu, H.; Sun, Z.; Luo, Z. Ionization and Dissociation of Benzene and Aniline under Deep Ultraviolet Laser Irradiation. Chin. J. Chem. Phys. 2020, 33 (5), 583– 589, DOI: 10.1063/1674-0068/cjcp2006086Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitlCmu7fI&md5=ec3291627cf9b23663668caad92ffa4fIonization and dissociation of benzene and aniline under deep ultraviolet laser irradiationGeng, Lijun; Zhang, Hanyu; Wu, Haiming; Sun, Zhendong; Luo, ZhixunChinese Journal of Chemical Physics (2020), 33 (5), 583-589CODEN: CJCPA6; ISSN:1674-0068. (American Institute of Physics)We report a study on photo-ionization of benzene and aniline with incidental subsequent dissocn. by the customized reflection time-of-flight mass spectrometer utilizing a deep UV 177.3 nm laser. Highly efficient ionization of benzene is obsd. with a weak C4H3+ fragment formed by undergoing disproportional C-C bond dissocn. In comparison, a major C5H6+· fragment and a minor C6H6+· radical are produced in the ionization of aniline pertaining to the removal of CNH· and NH· radicals, resp. First-principles calcn. is employed to reveal the photo-dissocn. pathways of these two mols. having a structural difference of just an amino group. It is demonstrated that hydrogen atom transfer plays an important role in the cleavage of C-C or C-N bonds in benzene and aniline ions. This study is helpful to understand the underlying mechanisms of chem. bond fracture of benzene ring and related arom. mols. (c) 2020 American Institute of Physics.
- 30Choe, J. C.; Cheong, N. R.; Park, S. M. Unimolecular Dissociation of Aniline Molecular Ion: A Theoretical Study. Int. J. Mass Spectrom. 2009, 279 (1), 25– 31, DOI: 10.1016/j.ijms.2008.09.013Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVCgsbvF&md5=f2de6768b1f47e62718a63fab73cbc13Unimolecular dissociation of aniline molecular ion: A theoretical studyChoe, Joong Chul; Cheong, Nu Ri; Park, Seung MinInternational Journal of Mass Spectrometry (2009), 279 (1), 25-31CODEN: IMSPF8; ISSN:1387-3806. (Elsevier B.V.)The potential energy surface (PES) for dissocn. of aniline ion was detd. using d. functional theory MO calcns. at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. On the basis of the PES obtained, kinetic anal. was performed by Rice-Ramsperger-Kassel-Marcus (RRKM) calcns. The RRKM dissocn. rate consts. agreed well with previous exptl. data. The most favorable channel was formation of the cyclopentadiene ion by loss of HNC, occurring through consecutive ring opening and re-closure to a five-membered ring. Loss of H· could compete with the HNC loss at high energy, which occurred by direct cleavage of an N-H bond or through ring expansion.
- 31Jusko, P.; Brünken, S.; Asvany, O.; Thorwirth, S.; Stoffels, A.; Van Der Meer, L.; Berden, G.; Redlich, B.; Oomens, J.; Schlemmer, S. The FELion Cryogenic Ion Trap Beam Line at the FELIX Free-Electron Laser Laboratory: Infrared Signatures of Primary Alcohol Cations. Faraday Discuss. 2019, 217, 172– 202, DOI: 10.1039/C8FD00225HGoogle Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXovFGktro%253D&md5=6b35e401a6040a672b855a985df71712The FELion cryogenic ion trap beam line at the FELIX free-electron laser laboratory: infrared signatures of primary alcohol cationsJusko, Pavol; Bruenken, Sandra; Asvany, Oskar; Thorwirth, Sven; Stoffels, Alexander; van der Meer, Lex; Berden, Giel; Redlich, Britta; Oomens, Jos; Schlemmer, StephanFaraday Discussions (2019), 217 (Advances in Ion Spectroscopy), 172-202CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)The combination of a 4 K 22-pole ion trap instrument, FELion, with the widely tunable free electron lasers at the FELIX Lab. is described in detail. It allows for wide-range IR vibrational spectroscopy of mol. ions. In this study, the app. is used for IR vibrational predissocn. (IR-PD) measurements of the simple alc. cations of methanol and ethanol as well as their protonated forms. Spectra are taken by tagging the cold mol. ions with He atoms. The IR spectrum of protonated methanol is recorded for the first time, and the wavelength coverage for all other species is substantially extended. The bands of all spectra are analyzed by comparison to ab initio calcn. results at different levels of theory. Vibrational bands of different isomers and conformers (rotamers) are discussed and identified in the exptl. spectra. Besides the measurement of IR-PD spectra, the method of IR multiple photon dissocn. IR-MPD is applied for some cases. Spectral narrowing due to the cold environment is obsd. and rotational band contours are simulated. This will help in identifying more complex species using the IR-MPD method in future measurements. Overall the IR-PD spectra reveal more bands than are obsd. for the IR-MPD spectra. In particular, many new bands are obsd. in the fingerprint region. Depletion satn. of the finite no. of trapped ions is obsd. for the IR-PD spectra of the ethanol cation and the presence of only one isomeric species is concluded. This special feature of ion trapping spectroscopy may be used in future studies for addressing specific isomers or cleaning the ion cloud from specific isomers or conformers. In addn., the results of this study can be used as a basis to obtain high-resoln. IR vibrational and THz rotational spectra of alc. ions in order to detect them in space.
- 32Oepts, D.; van der Meer, A. F. G.; van Amersfoort, P. W. The Free-Electron-Laser User Facility FELIX. Infrared Phys. Technol. 1995, 36 (1), 297– 308, DOI: 10.1016/1350-4495(94)00074-UGoogle Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXltlCksrg%253D&md5=45dfdce37069160f5527f00358a50e58The free-electron-laser user facility FELIXOepts, D.; van der Meer, A. F. G.; van Amersfoort, P. W.Infrared Physics & Technology (1995), 36 (1), 297-308CODEN: IPTEEY; ISSN:1350-4495.The Free Electron Laser for IR expts. FELIX presents to its users a versatile source of radiation in the IR and far-IR spectral regions. Presently, the wavelength range of operation extends 5-110 μm (2000-90 cm-1). The wavelength is continuously tunable over an octave in a few minutes. The output normally consists of macropulses of 5-10 μs duration, formed by a train of micropulses of a few ps length. Av. power in the macropulses is of order 10 kW, peak power in the micropulses is in the MW range. The temporal and spectral characteristics of the micropulses can be controlled by varying the synchronism between the electron pulses and the optical pulses circulating in the laser cavity. Transform-limited pulse lengths of 2-20 ps can be generated. Long-range coherence was induced by phase-locking successive micropulses, and narrow-band, essentially single-mode, radiation was selected from the output.
- 33Zeh, D.; Bast, M.; Rap, D. B.; Schmid, P. C.; Thorwirth, S.; Brünken, S.; Schlemmer, S.; Schäfer, M. Cryogenic Messenger-IR Ion Spectroscopy Study of Phenol & Aniline Molecular Ions and of the Common Fragment Ion [C5H6] •+ Formed by EI-MS. J. Mol. Spectrosc. 2021, 378, 111453, DOI: 10.1016/j.jms.2021.111453Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtVSgsrvI&md5=bf7f6ab8ea2321dfc3c552283da3bbe1Cryogenic Messenger-IR Ion Spectroscopy Study of Phenol & Aniline Molecular Ions and of the common Fragment Ion [C5H6]·+ formed by EI-MSZeh, Dennis; Bast, Marcel; Rap, Daniel B.; Schmid, Philipp C.; Thorwirth, Sven; Bruenken, Sandra; Schlemmer, Stephan; Schaefer, MathiasJournal of Molecular Spectroscopy (2021), 378 (), 111453CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Mol. ions of phenol and aniline as well as the fragment ion at m/z 66 formed by electron ionization are examd. with cryogenic messenger-IR ion spectroscopy and theory. According to the recorded IR spectra arom. ground state mol. ions of phenol and aniline are clearly identified. Similar to earlier reports our new set of spectroscopic and computational results supports the assumption that tautomeric mol. ions of phenol and aniline are only short-lived intermediates in the reaction path to the ultimate CO loss reaction product of phenol as well as the HNC loss product of aniline. Even the present cryogenic messenger-IR ion spectroscopy approach failed to collect spectroscopic evidence of the intermediate presence of these elusive tautomers of phenol and aniline mol. ions. However, our study clearly shows that the electron ionization mass spectrometry dissocn. product ion of phenol and aniline at m/z 66 is the cyclopentadiene radical cation [C5H6]·+ for the presence of which convincing spectroscopic evidence could be collected proving the structure assignment and identification. All messenger-IR ion spectroscopy expts. were conducted on a cryogenic 22-pole ion trap with the use of neon atoms for tagging. The MS instrument was coupled to a free electron laser delivering wavelength tunable IR radiation for spectroscopy. Harmonic and anharmonic force field calcns. complement the expts. and support band assignments of the recorded IR spectra and general data interpretation.
- 34Jusko, P.; Simon, A.; Wenzel, G.; Brünken, S.; Schlemmer, S.; Joblin, C. Identification of the Fragment of the 1-Methylpyrene Cation by Mid-IR Spectroscopy. Chem. Phys. Lett. 2018, 698, 206– 210, DOI: 10.1016/j.cplett.2018.03.028Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXltlWisrc%253D&md5=590c47b7e54525dcfe7a303739d927fcIdentification of the fragment of the 1-methylpyrene cation by mid-IR spectroscopyJusko, Pavol; Simon, Aude; Wenzel, Gabi; Brunken, Sandra; Schlemmer, Stephan; Joblin, ChristineChemical Physics Letters (2018), 698 (), 206-210CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)The fragment of the 1-methylpyrene cation, C17H+11, is expected to exist in two isomeric forms, 1-pyrenemethylium PyrCH+2 and the tropylium contg. species PyrC+7. We measured the IR action spectrum of cold C17H+11 tagged with Ne using a cryogenic ion trap instrument coupled to the FELIX laser. Comparison of the exptl. data with d. functional theory calcns. allows us to identify the PyrCH+2 isomer in our expts. The IR Multi-Photon Dissocn. spectrum was also recorded following the C2H2 loss channel. Its anal. suggests combined effects of anharmonicity and isomerisation while heating the trapped ions, as shown by mol. dynamics simulations.
- 35Gerlich, D. Inhomogeneous RF Fields: A Versatile Tool for the Study of Processes with Slow Ions. In Advances in Chemical Physics: State-Selected and State-To-State Ion-Molecule Reaction Dynamics, Part 1. Experiment; Wiley, 1992; Vol. 82; DOI: 10.1002/9780470141397.ch1 .Google ScholarThere is no corresponding record for this reference.
- 36Rap, D. B.; Marimuthu, A. N.; Redlich, B.; Brünken, S. Stable Isomeric Structures of the Pyridine Cation (C5H5N•+) and Protonated Pyridine (C5H5NH+) Elucidated by Cold Ion Infrared Spectroscopy. J. Mol. Spectrosc. 2020, 373, 111357, DOI: 10.1016/j.jms.2020.111357Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvVOmurfO&md5=d5142ab80b6626f6573dc57116cc358eStable isomeric structures of the pyridine cation (C5H5N+) and protonated pyridine (C5H5NH+) elucidated by cold ion infrared spectroscopyRap, Daniel B.; Marimuthu, Aravindh N.; Redlich, Britta; Bruenken, SandraJournal of Molecular Spectroscopy (2020), 373 (), 111357CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Cold ion action spectroscopy is applied to record the gas phase IR fingerprint spectra of mass-selected C5H5N•+ and C5H5NH+ cations using an IR free electron laser. The structures of the cations are deduced from the exptl. spectra using anharmonic vibrational frequencies from d. functional theory calcns. A very good agreement between exptl. and theor. IR frequencies is obsd. The dominant structure of the C5H5N•+ cation is assigned to the arom. pyridine radical cation form. Addnl., a minor contribution of the lower energetic α-distonic isomer is obsd. The C5H5NH+ cation is ascribed to the arom. pyridinium cation where protonation has taken place on the nitrogen atom. The rare-gas tag used in the action spectroscopic method has a negligible effect on the vibrational frequencies. The obsd. species, with now accurately detd. vibrational frequencies, are good candidates for future rotational spectroscopic studies and IR observations in astronomical sources such as interstellar clouds or Titan's atm.
- 37Marimuthu, A. N.; Sundelin, D.; Thorwirth, S.; Redlich, B.; Geppert, W. D.; Brünken, S. Laboratory Gas-Phase Vibrational Spectra of [C3H3]+ Isomers and Isotopologues by IRPD Spectroscopy. J. Mol. Spectrosc. 2020, 374, 111377, DOI: 10.1016/j.jms.2020.111377Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFegt7nN&md5=8cacaaa9e70f7ddbe83a2afcae58c37eLaboratory gas-phase vibrational spectra of [C3H3]+ isomers and isotopologues by IRPD spectroscopyMarimuthu, Aravindh N.; Sundelin, David; Thorwirth, Sven; Redlich, Britta; Geppert, Wolf D.; Brunken, SandraJournal of Molecular Spectroscopy (2020), 374 (), 111377CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Gas phase vibrational spectra of [C3H3]+ isomers and their fully deuterated isotopologues measured in a cryogenic 22-pole ion trap are presented. The widely tunable free electron laser for IR expts., FELIX, was employed to cover the frequency range 500-2400 cm-1, complemented with an OPO/OPA system covering 2800-3400 cm-1. Spectral assignments for both the linear and cyclic isomeric form (H2C3H+ and c-C3H+3, resp.) are made based on various high-level computational studies. The effect of ion source conditions and different precursors (allene and propargyl chloride) for the preferential prodn. of a specific isomer is discussed. The perturbation of the vibrational band position due to complexation with neon in the recorded IR-predissocn. (IRPD) spectra are also reported in this study.
- 38Marimuthu, A. N.; Huis in’t Veld, F.; Thorwirth, S.; Redlich, B.; Brünken, S. Infrared Predissociation Spectroscopy of Protonated Methyl Cyanide, CH3CNH+. J. Mol. Spectrosc. 2021, 379, 111477, DOI: 10.1016/j.jms.2021.111477Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXht1ehu7vJ&md5=72205daa46b9bf1f2ac4e5b184d96af9Infrared predissociation spectroscopy of protonated methyl cyanide, CH3CNH+Marimuthu, Aravindh N.; Huis in't Veld, Frank; Thorwirth, Sven; Redlich, Britta; Brunken, SandraJournal of Molecular Spectroscopy (2021), 379 (), 111477CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)The gas phase vibrational spectrum of CH3CNH+ is investigated using a messenger IR predissocn. (IRPD) action spectroscopic method. Vibrational bands were recorded in the 300-1700 cm-1 and 2000-3300 cm-1 regions making use of the widely tunable free electron laser for IR expts., FELIX, coupled to a cryogenic ion trap instrument. Band assignments were aided by high-level quantum-chem. calcns., which showed excellent agreement with the exptl. data. Effects of the neon atom used as messenger in the IRPD method are investigated in detail. The data presented here will support astronomical searches for the CH3CNH+ ion in space, and provide a basis for high-resoln. ro-vibrational and pure rotational studies in vibrationally excited states.
- 39Brünken, S.; Lipparini, F.; Stoffels, A.; Jusko, P.; Redlich, B.; Gauss, J.; Schlemmer, S. Gas-Phase Vibrational Spectroscopy of the Hydrocarbon Cations l-C3H+, HC3H+, and c-C3H2+: Structures, Isomers, and the Influence of Ne-Tagging. J. Phys. Chem. A 2019, 123 (37), 8053– 8062, DOI: 10.1021/acs.jpca.9b06176Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsF2ntL3P&md5=df5eb88bca69c7505159374a0a642371Gas-Phase Vibrational Spectroscopy of the Hydrocarbon Cations l-C3H+, HC3H+, and c-C3H2+: Structures, Isomers, and the Influence of Ne-TaggingBruenken, Sandra; Lipparini, Filippo; Stoffels, Alexander; Jusko, Pavol; Redlich, Britta; Gauss, Juergen; Schlemmer, StephanJournal of Physical Chemistry A (2019), 123 (37), 8053-8062CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)We report the first gas-phase vibrational spectra of the hydrocarbon ions C3H+ and C3H2+. The ions were produced by electron impact ionization of allene. Vibrational spectra of the mass-selected ions tagged with Ne were recorded using IR predissocn. spectroscopy in a cryogenic ion trap instrument using the intense and widely tunable radiation of a free electron laser. Comparison of high-level quantum chem. calcns. and resonant depletion measurements revealed that the C3H+ ion is exclusively formed in its most stable linear isomeric form, whereas two isomers were obsd. for C3H2+. Bands of the energetically favored cyclic c-C3H2+ are in excellent agreement with calcd. anharmonic frequencies, whereas for the linear open-shell HCCCH+ (2Πg) a detailed theor. description of the spectrum remains challenging because of Renner-Teller and spin-orbit interactions. Good agreement between theory and expt., however, is obsd. for the frequencies of the stretching modes for which an anharmonic treatment was possible. In the case of linear l-C3H+, small but non-negligible effects of the attached Ne on the ion fundamental band positions and the overall spectrum were found.
- 40Jusko, P.; Simon, A.; Banhatti, S.; Brünken, S.; Joblin, C. Direct Evidence of the Benzylium and Tropylium Cations as the Two Long-Lived Isomers of C7H7+. ChemPhysChem 2018, 19 (23), 3182– 3185, DOI: 10.1002/cphc.201800744Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFSrtLnO&md5=97dde1e9510d450c52293bbfe0595953Direct Evidence of the Benzylium and Tropylium Cations as the Two Long-Lived Isomers of C7H7+Jusko, Pavol; Simon, Aude; Banhatti, Shreyak; Bruenken, Sandra; Joblin, ChristineChemPhysChem (2018), 19 (23), 3182-3185CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Disentangling the isomeric structure of C7H7+ is a longstanding exptl. issue. We report here the full mid-IR vibrational spectrum of C7H7+ tagged with Ne obtained with IR-predissocn. spectroscopy at 10 K. Satn. depletion measurements were used to assign the contribution of benzylium and tropylium isomers and demonstrate that no other isomer is involved. Recorded spectral features compare well with d. functional theory calcns. This opens perspectives for a better understanding and control of the formation paths leading to either tropylium or benzylium ions.
- 41Frisch, M. J. G.; Trucks, W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Gaussian 16 , Rev. A.03; 2016.Google ScholarThere is no corresponding record for this reference.
- 42Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98 (7), 5648– 5652, DOI: 10.1063/1.464913Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXisVWgtrw%253D&md5=291bbfc119095338bb1624f0c21c7ca8Density-functional thermochemistry. III. The role of exact exchangeBecke, Axel D.Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.
- 43Barone, V.; Cimino, P.; Stendardo, E. Development and Validation of the B3LYP/N07D Computational Model for Structural Parameter and Magnetic Tensors of Large Free Radicals. J. Chem. Theory Comput. 2008, 4 (5), 751– 764, DOI: 10.1021/ct800034cGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXksVShtb0%253D&md5=deffc27472a7b65a612cea495fe022b8Development and Validation of the B3LYP/N07D Computational Model for Structural Parameter and Magnetic Tensors of Large Free RadicalsBarone, Vincenzo; Cimino, Paola; Stendardo, EmilianoJournal of Chemical Theory and Computation (2008), 4 (5), 751-764CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Extensive calcns. on a large set of free radicals contg. atoms of the second and third row show that the B3LYP/N07D computational model provides remarkably accurate structural parameters and magnetic tensors at reasonable computational costs. The key of this success is the optimization of core-valence s functions for hyperfine coupling consts., while retaining (and even improving) the good performances of the parent 6-31 + G(d,p) basis set for valence properties through reoptimization of polarization and diffuse p functions.
- 44Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132 (15), 154104, DOI: 10.1063/1.3382344Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXkvVyks7o%253D&md5=2bca89d904579d5565537a0820dc2ae8A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-PuGrimme, Stefan; Antony, Jens; Ehrlich, Stephan; Krieg, HelgeJournal of Chemical Physics (2010), 132 (15), 154104/1-154104/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The method of dispersion correction as an add-on to std. Kohn-Sham d. functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coeffs. and cutoff radii that are both computed from first principles. The coeffs. for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos. (CN). They are used to interpolate between dispersion coeffs. of atoms in different chem. environments. The method only requires adjustment of two global parameters for each d. functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of at. forces. Three-body nonadditivity terms are considered. The method has been assessed on std. benchmark sets for inter- and intramol. noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean abs. deviations for the S22 benchmark set of noncovalent interactions for 11 std. d. functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs. also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. (c) 2010 American Institute of Physics.
- 45Puzzarini, C.; Biczysko, M.; Barone, V. Accurate Harmonic/Anharmonic Vibrational Frequencies for Open-Shell Systems: Performances of the B3LYP/N07D Model for Semirigid Free Radicals Benchmarked by CCSD(T) Computations. J. Chem. Theory Comput. 2010, 6 (3), 828– 838, DOI: 10.1021/ct900594hGoogle Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFams7Y%253D&md5=6d985f98f3c56b2b28bffdce5d8a5d48Accurate Harmonic/Anharmonic Vibrational Frequencies for Open-Shell Systems: Performances of the B3LYP/N07D Model for Semirigid Free Radicals Benchmarked by CCSD(T) ComputationsPuzzarini, Cristina; Biczysko, Malgorzata; Barone, VincenzoJournal of Chemical Theory and Computation (2010), 6 (3), 828-838CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Impressive growth of computer facilities and effective implementation of very accurate quantum mech. methods allow, nowadays, the detn. of structures and vibrational characteristics for small- to medium-sized mols. to a very high accuracy. Since the situation is much less clear for open-shell species, we decided to build a suitable database of harmonic and anharmonic frequencies for small-sized free radicals contg. atoms of the first two rows of the periodic table. The level of theory employed is the CCSD(T) model in conjunction with triple- and quadruple-ζ basis sets, whose accuracy has been checked with respect to the available exptl. data and/or converged quantum mech. computations. Next, in view of studies of larger open-shell systems, we have validated the B3LYP/N07D model with ref. to the above database: our results confirm previous suggestions about the remarkable reliability and reduced computational cost of this computational method. A no. of test computations show that basis set extension has negligible effects and other d. functionals (including last generation ones) deliver significantly worse results. Increased accuracy can be obtained, instead, by using CCSD(T) harmonic frequencies and B3LYP/N07D anharmonic corrections.
- 46Lemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Mackie, C. J.; Candian, A.; Tielens, A. G. G. M.; Rijs, A. M.; Buma, W. J. Anharmonicity in the Mid-Infrared Spectra of Polycyclic Aromatic Hydrocarbons: Molecular Beam Spectroscopy and Calculations. Astron. Astrophys. 2019, 628, A130, DOI: 10.1051/0004-6361/201935631Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlOktbbJ&md5=54aa808993d11e69b7deba5abb1a1582Anharmonicity in the mid-infrared spectra of polycyclic aromatic hydrocarbons: molecular beam spectroscopy and calculationsLemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Mackie, C. J.; Candian, A.; Tielens, A. G. G. M.; Rijs, A. M.; Buma, W. J.Astronomy & Astrophysics (2019), 628 (), A130CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)Aims. In this work we det. the effects of anharmonicity on the mid-IR spectra of the linear polycyclic arom. hydrocarbons (PAHs) naphthalene, anthracene, tetracene and pentacene recorded using the free electron laser FELIX. Methods. Comparison of exptl. spectra obtained under supersonic jet conditions with theor. predicted spectra was used to show if anharmonicity explicitly needs to be taken into account. Results. Anharmonic spectra obtained using second-order vibrational perturbation theory agree on av. within 0.5% of the exptl. frequencies. Importantly, they confirm the presence of combination bands with appreciable intensity in the 5-6μm region. These combination bands contain a significant fraction of the IR absorption, which scales linearly with the size of the PAH. Detection and assignment of the combination bands are a preliminary indication of the accuracy of far-IR modes in our anharmonic theor. spectra. Detailed anal. of the periphery-sensitive CH out-of-plane band of naphthalene reveals that there is still room for improvement of the VPT2 approach. In addn., the implications of our findings for the anal. of the arom. IR bands are discussed.
- 47Montgomery, J. A.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A. A Complete Basis Set Model Chemistry. VII. Use of the Minimum Population Localization Method. J. Chem. Phys. 2000, 112 (15), 6532– 6542, DOI: 10.1063/1.481224Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitlSrsLc%253D&md5=af2e5c3f4d631ec7c98897040736828bA complete basis set model chemistry. VII. Use of the minimum population localization methodMontgomery, J. A., Jr.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A.Journal of Chemical Physics (2000), 112 (15), 6532-6542CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)It is shown that localization is necessary to preserve size consistency in nonlinear extrapolations of mol. energies. We demonstrate that the unphys. behavior of Mulliken populations obtained from extended basis set wave functions can lead to incomplete localization of orbitals by the Pipek-Mezey population localization method, and introduce a modification to correct this problem. The new localization procedure, called min. population localization, is incorporated into the CBS-QB3 and the new CBS-4M model chemistries, and their performance is assessed on the G2/97 test set. The errors found for CBS-QB3 are comparable with those for the G3 and G3(MP2) (mean abs. deviation of 1.10, 0.94, and 1.21 kcal/mol, resp., on the G2/97 test set). The CBS-4M is less accurate than the other models (mean abs. deviation of 3.26 kcal/mol on the G2/97 test set), but can be applied to much larger systems. The modified localization method resolves several problem cases found with CBS-4 and improves the reliability of CBS-QB3.
- 48Montgomery, J. A.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A. A Complete Basis Set Model Chemistry. VI. Use of Density Functional Geometries and Frequencies. J. Chem. Phys. 1999, 110 (2–12), 2822– 2827, DOI: 10.1063/1.477924Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXltlKntg%253D%253D&md5=f5da251681f5c1ba20c7268b98152415A complete basis set model chemistry. VI. Use of density functional geometries and frequenciesMontgomery, J. A., Jr.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A.Journal of Chemical Physics (1999), 110 (6), 2822-2827CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The recently introduced complete basis set, CBS-Q, model chem. is modified to use B3LYP hybrid d. functional geometries and frequencies, which give both improved reliability (max. error for the G2 test set reduced from 3.9 to 2.8 kcal/mol) and increased accuracy (mean abs. error reduced from 0.98 to 0.87 kcal/mol), with little penalty in computational speed. The use of a common method for geometries and frequencies makes the modified model applicable to transition states for chem. reactions.
- 49Smith, M. A.; Hager, J. W.; Wallace, S. C. Two Color Photoionization Spectroscopy of Jet Cooled Aniline: Vibrational Frequencies of the Aniline X̃2B1 Radical Cation. J. Chem. Phys. 1984, 80 (7), 3097– 3105, DOI: 10.1063/1.447124Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXitVSgsbg%253D&md5=70d0007df53e24b4c042161aff182cb5Two color photoionization spectroscopy of jet cooled aniline: vibrational frequencies of the aniline ~X2B1 radical cationSmith, Mark A.; Hager, James W.; Wallace, Stephen C.Journal of Chemical Physics (1984), 80 (7), 3097-105CODEN: JCPSA6; ISSN:0021-9606.Photoionization-efficiency spectra of free jet expansion cooled aniline in the 1B2 excited state were obtained by the technique of 2-color photoionization spectroscopy. The adiabatic ionization potential of rotationally cooled (<5 K) aniline is 62 265 ± 18 cm-1. By pumping a variety of vibronic transitions, photoionization-efficiency curves were obtained from discrete vibrational levels in the 1B2 state. The spectra generally show a strong propensity for vertical (Δv = 0) ionization. As a result, it was possible to det. the vibrational frequencies of the ground state aniline 2B1 radical cation with good precision for 6 vibrational modes. Vibrational progressions obsd. in the threshold curves support these assignments as well as allowing the observation of 2 addnl. modes in the ion which do not manifest themselves in the ‾A(1B2) ← ‾X(1A1) electronic spectrum. The magnitude of these vibrational frequencies compared to those known for the ground and 1st excited state of aniline suggest that the 2B1 ionic state is more rigidly planar than the 1B2 excited state.
- 50Lifshitz, C.; Malinovich, Y. Time Resolved Photoionization Mass Spectrometry in the Millisecond Range. Int. J. mass Spectrom. Ion Processes 1984, 60 (1), 99– 105, DOI: 10.1016/0168-1176(84)80078-6Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXlvVSrtr8%253D&md5=f2e285cf0ca26fe764d1a159a5d5064aTime resolved photoionization mass spectrometry in the millisecond rangeLifshitz, C.; Malinovich, Y.International Journal of Mass Spectrometry and Ion Processes (1984), 60 (), 99-105CODEN: IJMPDN; ISSN:0168-1176.A photoionization mass spectrometer operating in a time resolved manner, from the microsecond to the millisecond range, was constructed. A Hinteregger vacuum-UV light source is pulsed and the photoions produced are trapped in a cylindrical ion trap. Time resolved ionization efficiency curves are obtained. Several mols. which demonstrate large kinetic shifts were studied. Dissocn. rate coeffs. of ∼1 s-1 or lower were obsd. by using extended signal averaging techniques.
- 51Zaretskii, Z. V. I.; Oren, D.; Kelner, L. Automatic Method for the Measurement of the Electron Impact Ionization and Appearance Potentials. Appl. Spectrosc. 1976, 30 (3), 366– 368, DOI: 10.1366/000370276774457272Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE28XkslOjtro%253D&md5=5f07e2e9b0e1674c7792217fce0ebbceAutomatic method for the measurement of the electron impact ionization and appearance potentialsZaretskii, Ze'ev V. I.; Oren, David; Kelner, LeonidApplied Spectroscopy (1976), 30 (3), 366-8CODEN: APSPA4; ISSN:0003-7028.An automatic electronic scanner for the rapid recording of ionization efficiency curves was described.
- 52Lifshitz, C.; Gotchiguian, P.; Roller, R. Time-Dependent Mass Spectra and Breakdown Graphs. The Kinetic Shift in Aniline. Chem. Phys. Lett. 1983, 95 (2), 106– 108, DOI: 10.1016/0009-2614(83)85076-3Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXhtFKmsrc%253D&md5=f1c59eb984ec398326458aa69b528778Time-dependent mass spectra and breakdown graphs. The kinetic shift in anilineLifshitz, C.; Gotchiguian, P.; Roller, R.Chemical Physics Letters (1983), 95 (2), 106-8CODEN: CHPLBC; ISSN:0009-2614.Time-resolved appearance energies and metastable peak shapes were detd. by trapped-ion mass spectrometry (TIMS) for the unimol. dissocn. of aniline cations. The long-time (milliseconds) appearance energy (AE) limit, AE(C5H6+) = 11.26 ± 0.2 eV, suggests the formation at threshold energies of the cyclopentadienyl cation with neutral HNC.
- 53Rinehart, K. L.; Buchholz, A. C.; Van Lear, G. E. Mass Spectral Fragmentation of Aniline-1-13C. J. Am. Chem. Soc. 1968, 90 (4), 1073– 1075, DOI: 10.1021/ja01006a050Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXntleruw%253D%253D&md5=5bf834f9073f11cd14fc32b864d5d948Mass spectral fragmentation of aniline-1-carbon-13Rinehart, Kenneth L., Jr.; Buchholz, Allan C.; Van Lear, George E.Journal of the American Chemical Society (1968), 90 (4), 1073-5CODEN: JACSAT; ISSN:0002-7863.The low and high resoln. mass spectral peaks for PhNH2-1-13C were examd. The relative abundance of the isobaric peaks were measured. The results showed that most of the ions which have lost N have also lost 13C and most of those that retain N retain 13C. For the ions C5H6(-HCN) and C4H5N (-C2H2), as well as C4H3N, more than 90% of the ions arise from an unrearranged parent ion. C5H5+ and C4H4M+ are formed from C6H6N+ through the loss of HCN and C2H2, resp. The parent ion C6H7N is an odd electron ion which can lose either HCN and C2H2 directly or can rearrange to an even-electron ion while losing a H atom.
- 54Choe, J. C. Does the Gaseous Aniline Cation Isomerize to Methylpyridine Cations before Dissociation?. Bull. Korean Chem. Soc. 2013, 34 (11), 3249– 3252, DOI: 10.5012/bkcs.2013.34.11.3249Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFWqtLzF&md5=f84465a4e513c2f90026f277000c69caIsomerization of gaseous aniline cation to methylpyridine cations before dissociationChoe, Joong ChulBulletin of the Korean Chemical Society (2013), 34 (11), 3249-3252CODEN: BKCSDE; ISSN:0253-2964. (Korean Chemical Society)The potential energy surface for the isomerization of the aniline (AN) radical cation to the 2-, 3-, and 4-methylpyridine (picoline, MP) radical cations using G3 model calcns has been studied. The isomerization may occur through the 1H-azepine (7-aza-cycloheptatriene) radical cation. A quant. kinetic anal. has been performed using the Rice-Ramsperger-Kassel-Marcus theory, based on the potential energy surface. The result showed that isomerization between AN+ radical and each MP+ radical hardly occurs before their dissocns.
- 55Hedaya, E.; Kent, M. E.; McNeil, D. W.; Lossing, F. P.; McAllister, T. The Thermal Rearrangement of Phenylnitrene to Cyanocyclopentadiene. Tetrahedron Lett. 1968, 9 (30), 3415– 3420, DOI: 10.1016/S0040-4039(00)89507-6Google ScholarThere is no corresponding record for this reference.
- 56Vuitton, V.; Yelle, R. V.; Klippenstein, S. J.; Hörst, S. M.; Lavvas, P. Simulating the Density of Organic Species in the Atmosphere of Titan with a Coupled Ion-Neutral Photochemical Model. Icarus 2019, 324, 120– 197, DOI: 10.1016/j.icarus.2018.06.013Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktVKntrk%253D&md5=2ebec19e2c2cdc8671c887bb0769bcbcSimulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical modelVuitton, V.; Yelle, R. V.; Klippenstein, S. J.; Horst, S. M.; Lavvas, P.Icarus (2019), 324 (), 120-197CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)We present a one-dimensional coupled ion-neutral photochem. kinetics and diffusion model to study the atm. compn. of Titan in light of new theor. kinetics calcns. and scientific findings from the Cassini-Huygens mission. The model extends from the surface to the exobase. The atm. background, boundary conditions, vertical transport and aerosol opacity are all constrained by the Cassini-Huygens observations. The chem. network includes reactions between hydrocarbons, nitrogen and oxygen bearing species. It takes into account neutrals and both pos. and neg. ions with masses extending up to 116 and 74 u, resp. We incorporate high-resoln. isotopic photoabsorption and photodissocn. cross sections for N2 as well as new photodissocn. branching ratios for CH4 and C2H2. Ab initio transition state theory calcns. are performed in order to est. the rate coeffs. and products for crit. reactions. Main reactions of prodn. and loss for neutrals and ions are quant. assessed and thoroughly discussed. The vertical distributions of neutrals and ions predicted by the model generally reproduce observational data, suggesting that for the small species most chem. processes in Titan's atm. and ionosphere are adequately described and understood; some differences are highlighted. Notable remaining issues include (i) the total pos. ion d. (essentially HCNH+) in the upper ionosphere, (ii) the low mass neg. ion densities (CN-,C3N-/C4H-) in the upper atm., and (iii) the minor oxygen-bearing species (CO2, H2O) d. in the stratosphere. Pathways towards complex mols. and the impact of aerosols (UV shielding, at. and mol. hydrogen budget, nitriles heterogeneous chem. and condensation) are evaluated in the model, along with lifetimes and solar cycle variations.
- 57Dubois, D.; Carrasco, N.; Jovanovic, L.; Vettier, L.; Gautier, T.; Westlake, J. Positive Ion Chemistry in an N2-CH4 Plasma Discharge: Key Precursors to the Growth of Titan Tholins. Icarus 2020, 338, 113437, DOI: 10.1016/j.icarus.2019.113437Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisFSrsrbE&md5=e816d28bdf36b79137c66407225e382fPositive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholinsDubois, David; Carrasco, Nathalie; Jovanovic, Lora; Vettier, Ludovic; Gautier, Thomas; Westlake, JosephIcarus (2020), 338 (), 113437CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)Titan is unique in the solar system as it hosts a dense atm. mainly made of mol. nitrogen N2 and methane CH4. The Cassini Huygens Mission revealed the presence of an intense atm. photochem. initiated by the photo dissocn. and ionization of N2 and CH4. In the upper atm., Cassini detected signatures compatible with the presence of heavily charged mols. which are precursors for the solid core of the aerosols. These observations have indicated that ion chem. has an important role for org. growth. However, the processes coupling ion chem. and aerosol formation and growth are still mostly unknown. In this study, we investigated the cation chem. responsible for an efficient org. growth that we observe in Titan's upper atm., simulated using the PAMPRE plasma reactor. Pos. ion precursors were measured by in situ ion mass spectrometry in a cold plasma and compared with INMS observations taken during the T40 flyby. A series of pos. ion measurements were performed in three CH4 mixing ratios (1%, 5% and 10%) showing a variability in ion population. Low methane concns. result in an abundance of amine cations such as NH+4 whereas aliph. compds. dominate at higher methane concns. In conditions of favored tholin prodn., the presence of C2 compds. such as HCNH+ and C2H+5 is found to be consistent with copolymeric growth structures seen in tholin material. The obsd. abundance of these two ions particularly in conditions with lower CH4 amts. is consistent with modeling work simulating aerosol growth in Titan's ionosphere, which includes mass exchange primarily between HCNH+ and C2H+5 and neg. charged particles. These results also confirm the prevalent role of C2 cations as precursors to mol. growth and subsequent mass transfer to the charged aerosol particles as the CH4 abundance decreases towards lower altitudes.
- 58Lavvas, P.; Galand, M.; Yelle, R. V.; Heays, A. N.; Lewis, B. R.; Lewis, G. R.; Coates, A. J. Energy Deposition and Primary Chemical Products in Titan’s Upper Atmosphere. Icarus 2011, 213 (1), 233– 251, DOI: 10.1016/j.icarus.2011.03.001Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXltlGgu7Y%253D&md5=a50aa0409b282d6ec14b86c86aa01d57Energy deposition and primary chemical products in Titan's upper atmosphereLavvas, P.; Galand, M.; Yelle, R. V.; Heays, A. N.; Lewis, B. R.; Lewis, G. R.; Coates, A. J.Icarus (2011), 213 (1), 233-251CODEN: ICRSA5; ISSN:0019-1035. (Elsevier B.V.)Cassini results indicate that solar photons dominate energy deposition in Titan's upper atm. These dissoc. and ionize nitrogen and methane and drive the subsequent complex org. chem. The improved constraints on the atm. compn. from Cassini measurements demand greater precision in the photochem. modeling. Therefore, in order to quantify the role of solar radiation in the primary chem. prodn., we have performed detailed calcns. for the energy deposition of photons and photoelectrons in the atm. of Titan and we validate our results with the Cassini measurements for the electron fluxes and the EUV/FUV emissions. We use high-resoln. cross sections for the neutral photodissocn. of N2, which we present here, and show that they provide a different picture of energy deposition compared to results based on low-resoln. cross sections. Furthermore, we introduce a simple model for the energy degrdn. of photoelectrons based on the local deposition approxn. and show that our results are in agreement with detailed calcns. including transport, in the altitude region below 1200 km, where the effects of transport are negligible. Our calcd., daytime, electron fluxes are in good agreement with the measured fluxes by the Cassini Plasma Spectrometer (CAPS), and the same holds for the measured FUV emissions by the UV Imaging Spectrometer (UVIS). Finally, we present the vertical prodn. profiles of radicals and ions originating from the interaction of photons and electrons with the main components of Titan's atm., along with the column integrated prodn. rates at different solar zenith angles. These can be used as basis for any further photochem. calcns.
- 59Galand, M.; Yelle, R.; Cui, J.; Wahlund, J. E.; Vuitton, V.; Wellbrock, A.; Coates, A. Ionization Sources in Titan’s Deep Ionosphere. J. Geophys. Res. Space Phys. 2010, 115 (7), 7312, DOI: 10.1029/2009JA015100Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlWrsbbK&md5=404eef0f463585494baabfdeac44732dIonization sources in Titan's deep ionosphereGaland, Marina; Yelle, Roger; Cui, Jun; Wahlund, Jan-Erik; Vuitton, Veronique; Wellbrock, Anne; Coates, AndrewJournal of Geophysical Research, [Space Physics] (2010), 115 (A7), A07312/1-A07312/14CODEN: JJGPD4 ISSN:. (American Geophysical Union)We analyze a multi-instrumental data set from four Titan encounters by the Cassini spacecraft to investigate in detail the formation of the ionosphere. The data set includes observations of thermospheric and ionospheric species and suprathermal electrons. A model describing the solar and electron energy deposition is used as an organizing element of the Cassini data set. We first compare the calcd. secondary electron prodn. rates with the rates inferred from suprathermal electron intensity measurements. We then calc. an effective electron dissociative recombination coeff., applying three different approaches to the Cassini data set. Our findings are threefold: (1) The effective recombination coeff. derived under sunlit conditions in the deep ionosphere (<1200 km) is found to be independent of solar zenith angle and flyby. Its value ranges from 6.9 × 10-7 cm3 s-1 at 1200 km to 5.9 × 10-6 cm3 s-1 at 970 km at 500 K. (2) The presence of an addnl., minor source of ionization is revealed when the solar contribution is weak enough. The contribution by this non-solar source-energetic electrons most probably of magnetospheric origin-becomes apparent for secondary electron prodn. rates, due to solar illumination alone, close to or smaller than about 3 × 10-1 cm-3 s-1. Such a threshold is reached near the solar terminator below the main solar-driven electron prodn. peak (<1050 km). (3) Our ability to model the electron d. in the deep ionosphere is very limited. Our findings highlight the need for more lab. measurements of electron dissociative recombination coeffs. for heavy ion species at high electron temps. (esp. near 500 K).
- 60Puzzarini, C.; Barone, V. A Never-Ending Story in the Sky: The Secrets of Chemical Evolution. Phys. Life Rev. 2020, 32, 59– 94, DOI: 10.1016/j.plrev.2019.07.001Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3MzovVSjsg%253D%253D&md5=2bea3a3f04dd5d61d3088c1bb572c57bA never-ending story in the sky: The secrets of chemical evolutionPuzzarini Cristina; Barone VincenzoPhysics of life reviews (2020), 32 (), 59-94 ISSN:.Cosmic evolution is the tale of progressive transition from simplicity to complexity. The newborn universe started with the simplest atoms formed after the Big Bang and proceeded toward the formation of the so-called 'astronomical complex organic molecules' (aCOMs), most of them showing a clear prebiotic character. Understanding the chemical evolution of the universe is one of the main aims of Astrochemistry, with the starting point being the knowledge whether a molecule is present in the astronomical environment under consideration and, if so, its abundance. However, the interpretation of astronomical detections and the identification of molecules are not at all straightforward. Indeed, the extraterrestrial chemical inventory has been obtained by means of astronomical observations based on spectroscopic signatures determined in laboratory (either experimental or computational) studies. Even though the presence of aCOMs has been known for decades, the processes that lead to their synthesis are still hotly debated or even unknown. It is often assumed that aCOMs are mostly synthesized on grain surfaces during the so-called warm-up phase, when various radicals trapped in the grain mantles acquire mobility and recombine into large molecules. However, recent detections of aCOMs in cold environments have challenged this exclusive role of grain-surface chemistry. Clearly, gas-phase chemistry is at work in cold environments. Moving to Titan's atmosphere, prior to the Cassini-Huygens arrival in the Saturn system, it was generally believed that Earth and interstellar space are the two places where organic molecules are/were synthesized extensively. However, the experimental measurements by the instruments on board the Cassini orbiter spacecraft and the Huygens probe lander have changed this view. To disclose the "secrets" of chemical evolution across space, the first step is the understanding of how small prebiotic species are formed and how the chemical complexity can further increase. This review indeed addresses the chemical evolution in space, focusing - in particular - on the role played by molecular spectroscopy and quantum-chemical computations. To summarize, in this review we will first of all present how the signatures of molecules can be found in space. Then, we will address, from a computational point of view, the derivation of the molecular spectroscopic features, the investigation of gas-phase formation routes of prebiotic species in the ISM, and the evolution of chemical complexity, from small molecules to haze, in Titan's atmosphere. Finally, an integrated strategy, also involving high-performance computers and virtual reality, will be discussed.
- 61Hendrix, J.; Bera, P. P.; Lee, T. J.; Head-Gordon, M. Cation, Anion, and Radical Isomers of C4H4N: Computational Characterization and Implications for Astrophysical and Planetary Environments. J. Phys. Chem. A 2020, 124 (10), 2001– 2013, DOI: 10.1021/acs.jpca.9b11305Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjsV2mtbw%253D&md5=268549e5488895704e5c72dbc1587b1cCation, Anion, and Radical Isomers of C4H4N: Computational Characterization and Implications for Astrophysical and Planetary EnvironmentsHendrix, Josie; Bera, Partha P.; Lee, Timothy J.; Head-Gordon, MartinJournal of Physical Chemistry A (2020), 124 (10), 2001-2013CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)Nitrogen-contg. ions and mols. in the gas phase have been detected in non-Earth environments such as dark mol. clouds and more recently in the atm. of Saturn's moon Titan. These mols. may serve as precursors to larger heterocyclic structures that provide the foundation of complex biol. mols. On Titan, mols. of m/z 66 have been detected by the Cassini mission, and species of the empirical formula C4H4N may contribute to this signature. We have characterized seven isomers of C4H4N in anionic, neutral radical, and cationic states using d. functional theory. Structures were optimized using the range-sepd. hybrid ωB97X-V with the cc-pVTZ and aug-cc-pVTZ basis sets. Anionic and radical C4H4N favor cyclic structures with arom. and quasi-arom. electron arrangements, resp. Interestingly, ionization from the radical surface to the cation induces significant changes in structural stability, and the global min. for pos. charged isomers is CH2CCHCNH+, a pseudo-linear species reminiscent of cyanoallene. Select formation pathways to these structures from Titan's existing or postulated gas-phase species, reactions that are also relevant for other astrophys. environments, are discussed. By characterizing C4H4N isomers, we have identified energetically stable anionic, radical, and cationic structures that may be present in Titan's atm. and dark mol. clouds.
- 62Dobrijevic, M.; Loison, J. C.; Hickson, K. M.; Gronoff, G. 1D-Coupled Photochemical Model of Neutrals, Cations and Anions in the Atmosphere of Titan. Icarus 2016, 268, 313– 339, DOI: 10.1016/j.icarus.2015.12.045Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlaju7k%253D&md5=adb4d23fb21e2b8fa006395f643f6e4e1D-coupled photochemical model of neutrals, cations and anions in the atmosphere of TitanDobrijevic, M.; Loison, J. C.; Hickson, K. M.; Gronoff, G.Icarus (2016), 268 (), 313-339CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)Many models with different characteristics have been published so far to study the chem. processes at work in Titan's atm. Some models focus on neutral species in the stratosphere or ionic species in the ionosphere, but few of them couple all the species throughout the whole atm. Very few of these emphasize the importance of uncertainties in the chem. scheme and study their propagation in the model.We have developed a new 1D-photochem. model of Titan's atm. coupling neutral species with pos. and neg. ions from the lower atm. up to the ionosphere and have compared our results with observations to have a comprehensive view of the chem. processes driving the compn. of the stratosphere and ionosphere of Titan. We have updated the neutral, pos. ion and neg. ion chem. and have improved the description of N2 photodissocn. by introducing high resoln. N2 absorption cross sections. We performed for the first time an uncertainty propagation study in a fully coupled ion-neutral model.We det. how uncertainties on rate consts. on both neutral and ionic reactions influence the model results and pinpoint the key reactions responsible for this behavior. We find very good agreement between our model results and observations in both the stratosphere and in the ionosphere for most neutral compds. COur results are also in good agreement with an av. INMS mass spectrum and specific flybys in the dayside, suggesting that our chem. model (for both neutral and ions) provides a good approxn. of Titan's atm. chem. as a whole. Our uncertainty propagation study highlights the difficulty to interpret the INMS mass spectra for masses 14, 31, 41 and we identified the key reactions responsible for these ambiguities.Despite an overall improvement in the chem. model, disagreement for some specific compds. (HC3N, C2H5CN, C2H4) highlights the role that certain phys. processes could play (meridional dynamics or sticking on aerosols). We find that some crit. key reactions are important for many compds. including both neutrals and ions and should be studied in priority to lower the remaining model uncertainties. Extensive studies for some specific processes (including photolyses) are required.
- 63De Haas, A. J.; Oomens, J.; Bouwman, J. Facile Pentagon Formation in the Dissociation of Polyaromatics. Phys. Chem. Chem. Phys. 2017, 19 (4), 2974– 2980, DOI: 10.1039/C6CP08349HGoogle Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFehtbrM&md5=1c6afb975e816910eae3431d2f381ff2Facile pentagon formation in the dissociation of polyaromaticsde Haas, Arjen J.; Oomens, Jos; Bouwman, JordyPhysical Chemistry Chemical Physics (2017), 19 (4), 2974-2980CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Energetic processing of gaseous polycyclic arom. hydrocarbons (PAHs) plays a pivotal role in the chemistries of inter- and circumstellar environments, certain planetary atmospheres, and also in the chem. of combustion and soot formation. Although the precursor PAH species have been extensively characterized, the products from these gaseous breakdown reactions have received far less attention. It has been particularly challenging to accurately det. their mol. structure in gas-phase expts., where comparisons against theor. modeling are best made. Here we report on a combined exptl. and theor. study of the dissociative ionization of two nitrogen contg. polycyclic arom. hydrocarbons of C13H9N compn., acridine and phenanthridine. The structures of HCN-loss fragments are resolved by IR multiple-photon dissocn. (IRMPD) spectroscopy of the mass-isolated products in an ion trap mass spectrometer. Quantum-chem. computations as well as ref. IRMPD spectra are employed to unambiguously identify the mol. structures. Furthermore, computations at the d. functional level of theory provide insight into chem. pathways leading to the obsd. products. Acenaphthylene·+ and benzopentalene·+ - two arom. species contg. pentagons - are identified as the main products, suggesting that such species are easily formed and may be abundant in regions where thermal or photoprocessing of polyaroms. occurs.
- 64Marciniak, A.; Joblin, C.; Mulas, G.; Mundlapati, V. R.; Bonnamy, A. Photodissociation of Aliphatic PAH Derivatives under Relevant Astrophysical Conditions. Astron. Astrophys. 2021, 652, A42, DOI: 10.1051/0004-6361/202140737Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitFyhsbjN&md5=ff4423faab446b974c869602fc692c02Photodissociation of aliphatic PAH derivatives under relevant astrophysical conditionsMarciniak, A.; Joblin, C.; Mulas, G.; Mundlapati, V. Rao; Bonnamy, A.Astronomy & Astrophysics (2021), 652 (), A42CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)The interaction of polycyclic arom. hydrocarbons (PAHs) with vacuum UV (VUV) photons triggers the emission of the well-known arom. IR bands (AIBs), but other mechanisms, such as fragmentation, can be involved in this interaction. Fragmentation leads to selection effects that favor specific sizes and structures. Our aim is to investigate the impact of aliph. bonds on the VUV photostability of PAH cations in a cryogenic and collisionless environment with conditions applicable for photodissocn. regions (PDRs). The studied species are derived from pyrene (C16H10) and coronene (C24H12) and contain aliph. bonds either in the form of Me or Et sidegroups or of superhydrogenation. Their cations are produced by laser desorption ionization and isolated in the cryogenic ion cell of the PIRENEA setup, where they are submitted to VUV photons of 10.5 eV energy over long timescales (∼1000 s). The parent and fragment ions are mass-analyzed and their relative intensities are recorded as a function of the irradn. time. The fragmentation cascades are analyzed with a simple kinetics model from which we identify fragmentation pathways and derive fragmentation rates and branching ratios for both the parents and their main fragments. Aliph. PAH derivs. are found to have a higher fragmentation rate and a higher carbon to hydrogen loss compared to regular PAHs. On the other hand, the fragmentation of PAHs with alkylated sidegroups forms species with peripheral pentagonal cycles, which can be as stable as, or even more stable than, the bare PAH cations. This stability is quantified for the main ions involved in the fragmentation cascades by the comparison of the fragmentation rates with the photoabsorption rates derived from theor. photoabsorption cross sections. The most stable species for which there is an effective competition of fragmentation with isomerization and radiative cooling are identified, providing clues on the structures favored in PDRs. Conclusions. This work supports a scenario in which the evapn. of nanograins with a mixed aliph. and arom. compn. followed by VUV photoprocessing results in both the prodn. of the carriers of the 3.4 μm AIB by Me sidegroups and in an abundant source of small hydrocarbons at the border of PDRs. An addnl. side effect is the efficient formation of stable PAHs that contain some peripheral pentagonal rings. Our expts. also support the role of isomerization processes in PAH photofragmentation, including the H-migration process, which could lead to an addnl. contribution to the 3.4 μm AIB.
- 65Rodriguez Castillo, S.; Simon, A.; Joblin, C. Investigating the Importance of Edge-Structure in the Loss of H/H2 of PAH Cations: The Case of Dibenzopyrene Isomers. Int. J. Mass Spectrom. 2018, 429, 189– 197, DOI: 10.1016/j.ijms.2017.09.013Google Scholar65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslehtrfF&md5=a1061550b03f54d90d93212f5e8d92e8Investigating the importance of edge-structure in the loss of H/H2 of PAH cations: The case of dibenzopyrene isomersRodriguez Castillo, Sarah; Simon, Aude; Joblin, ChristineInternational Journal of Mass Spectrometry (2018), 429 (), 189-197CODEN: IMSPF8; ISSN:1387-3806. (Elsevier B.V.)We present a detailed study of the main dehydrogenation processes of two dibenzopyrene cation (C24H+14) isomers, namely dibenzo(a,e)pyrene (AE+) and dibenzo(a,l)pyrene (AL+). First, action spectroscopy under VUV photons was performed using synchrotron radiation in the 8-20 eV range. We obsd. lower dissocn. thresholds for the non-planar mol. (AL+) than for the planar one (AE+) for the main dissocn. pathways: H and 2H/H2 loss. In order to rationalize the exptl. results, dissocn. paths were investigated by means of d. functional theory calcns. In the case of H loss, which is the dominant channel at the lowest energies, the obsd. difference between the two isomers can be explained by the presence in AL+ of two C-H bonds with considerably lower adiabatic dissocn. energies. In both isomers the 2H/H2 loss channels are obsd. only at about 1 eV higher than H loss. We suggest that this is due to the propensity of bay H atoms to easily form H2. In addn., in the case of AL+, we cannot exclude a competition between 2H and H2 channels. In particular, the formation of a stable dissocn. product with a five-membered ring could account for the low energy sequential loss of 2 hydrogens. This work shows the potential role of non-compact PAHs contg. bay regions in the prodn. of H2 in space.
- 66Cernicharo, J.; Agúndez, M.; Kaiser, R. I.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; De Vicente, P. Discovery of Two Isomers of Ethynyl Cyclopentadiene in TMC-1: Abundances of CCH and CN Derivatives of Hydrocarbon Cycles. Astron. Astrophys. 2021, 655, L1, DOI: 10.1051/0004-6361/202142226Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XitVWltr8%253D&md5=b18da27021abbe28603d962096606617Discovery of two isomers of ethynyl cyclopentadiene in TMC-1 and abundances of CCH and CN derivatives of hydrocarbon cyclesCernicharo, J.; Agundez, M.; Kaiser, R. I.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; de Vicente, P.Astronomy & Astrophysics (2021), 655 (), L1CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)We report the detection of two isomers of ethynyl cyclopentadiene (c-C5H5CCH), namely 1- and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4 ± 0.2) x 1012 cm-2 and (2.0 ± 0.4) x 1012 cm-2, resp., for these two cyclopentadiene derivs., which imply that they are about ten times less abundant than cyclopentadiene. We also report the tentative detection of ethynyl benzene (C6H5CCH), for which we est. a column d. of (2.5 ± 0.4) x 1012 cm-2. We derived abundances for the corresponding cyano derivs. of cyclopentadiene and benzene and found values significantly lower than previously reported. The rotational temp. of the ethynyl and cyano derivs. of these cycles is about 9 K, i.e., very close to the gas kinetic temp. of the cloud. The abundance ratio of the 1- and 2-isomers of ethynyl cyclopentadiene is 1.4 ± 0.5, while for the two isomers of cyano cyclopentadiene it is 2.4 ± 0.6. The relative abundances of CCH over CN derivs. is 7.7 ± 2.2 for cyclopentadiene, which probably reflects the abundance ratio of the radicals CCH and CN; this ratio is only 2.1 ± 0.5 for benzene, which suggests that addnl. reactions besides cyano radicals with benzene are involved in the formation of benzonitrile. The formation of these cycles is reasonably well accounted for through a chem. scheme based on neutral-neutral reactions. It is predicted that benzene should be as abundant as cyclopentadiene in TMC-1.
- 67Cernicharo, J.; Marcelino, N.; Agúndez, M.; Endo, Y.; Cabezas, C.; Bermúdez, C.; Tercero, B.; De Vicente, P. Discovery of HC3O+ in Space: The Chemistry of O-Bearing Species in TMC-1. Astron. Astrophys. 2020, 642, L17, DOI: 10.1051/0004-6361/202039351Google ScholarThere is no corresponding record for this reference.
- 68Hunter, E. P. L.; Lias, S. G. Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update. J. Phys. Chem. Ref. Data 1998, 27 (3), 413– 656, DOI: 10.1063/1.556018Google Scholar68https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXjvVKgtLs%253D&md5=4dc92e07c2bc4f423b644c8ca54aca3aEvaluated Gas Phase Basicities and Proton Affinities of Molecules: An UpdateHunter, Edward P. L.; Lias, Sharon G.Journal of Physical and Chemical Reference Data (1998), 27 (3), 413-656CODEN: JPCRBU; ISSN:0047-2689. (American Chemical Society)A review with more than 70 refs. The available data on gas-phase basicities and proton affinities of approx. 1700 mol., radical, and at. neutral species are evaluated and compiled. Tables of the data are sorted (1) according to empirical formula and (2) according to evaluated gas basicity. This publication constitutes an update of a similar evaluation published in 1984.
- 69Botschwina, P. A Theoretical Investigation of the Astrophysically Important Molecules C3O and HC3O+. J. Chem. Phys. 1989, 90 (8), 4301– 4312, DOI: 10.1063/1.455787Google Scholar69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXks1Cgt7w%253D&md5=1d265443795c5fea6a32756ec7b60dc6A theoretical investigation of the astrophysically important molecules tricarbon monoxide and protonated tricarbon monoxide (C3O and HC3O+)Botschwina, PeterJournal of Chemical Physics (1989), 90 (8), 4301-13CODEN: JCPSA6; ISSN:0021-9606.Large-scale CEPA calcns. were carried out for the astrophys. important mols. C3O and HC3O+. C3O has a linear equil. geometry with short terminal CC and CO bond lengths of 1.273 and 1.149 Å and a central CC equil. bond length of 1.300 Å. Upon protonation the terminal CC and CO bond lengths are shortened by 0.061 and 0.026 Å, resp., while the central CC bond length experiences an elongation by 0.052 Å. C3O has a noticeably large equil. dipole moment of 2.535 D with the pos. end at the oxygen site. The IR intensity of the ν1 band at 2229 cm-1 is extremely large (72 756 cm2 mol-1). Although the intensity of the corresponding ν2 band of HC3O+ at 2318 cm-1 is only about one half as large this band appears to be most promising for future IR diode laser investigation. The proton affinity of C3O at 298 K is 885 ± 5 kJ mol-1.
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Abstract
Figure 1
Figure 1. Experimental mass spectra showing the ionization and fragmentation of aniline in (a) the storage ion source at 40 eV and (b) the direct electron impact source at electron energies of 20 eV (33) (black) and 50 eV (pink). The most important fragmentation channels C6H6N+ (m/z 92, H loss), C5H6•+ (m/z 66, HNC loss), and C5H5+ or C4H3N•+ (m/z 65, HNCH or C2H4 loss) are labeled.
Figure 2
Figure 2. Experimental infrared predissociation spectrum of C6H6N+–Ne (gray) and calculated anharmonic infrared spectra of H-1-cyano-CPD+ (pink) and H-2-cyano-CPD+ (blue) plotted with sticks. The inset shows a close-up of the lower wavenumber region. The B3LYP-GD3/N07D level of theory was used to optimize the geometries of the two isomers and calculate the vibrational frequencies.
Figure 3
Figure 3. Overview of the different fragmentation pathways of aniline•+ via (pathway 1) direct H loss, (pathway 3) isomerization and HNC loss, and (pathways 2 and 4) isomerization and H loss. The potential energy surface was evaluated using the CBS-QB3 method. The zero-point corrected electronic energies are given relative to aniline•+ (1) in kJ/mol between parentheses for minima and above the arrows for transitions states, respectively. The structures observed here are colored in pink and blue according to the structures 11 and 12 from Figure 2, respectively.
Figure 4
Figure 4. Experimental infrared spectrum of m/z 92 (gray) and comparison with the calculated anharmonic frequencies of (a) anilino+ (red), (b) 1-dehydro-aniline+ (green), (c) azatropylium+ (blue), and (d) H-5-cyano-CPD+ (brown).
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- 4Campbell, E. K.; Holz, M.; Gerlich, D.; Maier, J. P. Laboratory Confirmation of C60+ as the Carrier of Two Diffuse Interstellar Bands. Nature 2015, 523 (7560), 322– 323, DOI: 10.1038/nature145664https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFyks7jJ&md5=67ac7a689e1d55a9936645ebb5de4954Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bandsCampbell, E. K.; Holz, M.; Gerlich, D.; Maier, J. P.Nature (London, United Kingdom) (2015), 523 (7560), 322-323CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)The diffuse interstellar bands are absorption lines seen towards reddened stars. None of the mols. responsible for these bands were conclusively identified. Two bands at 9,632 and 9,577 Å were reported in 1994, and probably arise from C60+ mols., from the proximity of these wavelengths to the absorption bands of C60+ measured in a Ne matrix. Confirmation of this assignment requires the gas-phase spectrum of C60+. Lab. spectroscopy of C60+ in the gas phase, cooled to 5.8 K is reported. The absorption spectrum has max. at 9,632.7 ± 0.1 and 9,577.5 ± 0.1 Å, and the full widths at half-max. of these bands are 2.2 ± 0.2 and 2.5 ± 0.2 Å, resp. The diffuse interstellar bands at 9,632 Å and 9,577 Å are pos. identified as arising from C60+ in the interstellar medium.
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- 6McGuire, B. A.; Loomis, R. A.; Burkhardt, A. M.; Lee, K. L. K.; Shingledecker, C. N.; Charnley, S. B.; Cooke, I. R.; Cordiner, M. A.; Herbst, E.; Kalenskii, S. Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering. Science (1979) 2021, 371 (6535), 1265– 1269, DOI: 10.1126/science.abb7535There is no corresponding record for this reference.
- 7Cernicharo, J.; Agúndez, M.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; de Vicente, P. Pure Hydrocarbon Cycles in TMC-1: Discovery of Ethynyl Cyclopropenylidene, Cyclopentadiene, and Indene. Astron. Astrophys. 2021, 649, L15, DOI: 10.1051/0004-6361/2021411567https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsl2iu7%252FP&md5=7095ed65a79127ff2f1a6fcc4b56fb50Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene, and indeneCernicharo, J.; Agundez, M.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; De Vicente, P.Astronomy & Astrophysics (2021), 649 (), L15CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)We report the detection for the first time in space of three new pure hydrocarbon cycles in TMC-1: c-C3HCCH (ethynyl cyclopropenylidene), c-C5H6 (cyclopentadiene), and c-C9H8 (indene). We derive a column d. of 3.1 x 1011 cm-2 for the first cycle and similar values, in the range (1 -2) x 1013 cm-2, for the second and third. This means that cyclopentadiene and indene, in spite of their large size, are exceptionally abundant, only a factor of five less abundant than the ubiquitous cyclic hydrocarbon c-C3H2. The high abundance found for these two hydrocarbon cycles together with the high abundance previously found for the propargyl radical (CH2CCH) and other hydrocarbons, such as vinyl and allenyl acetylene (Agundez et al. 2021, A&A, 647, L10; Cernicharo et al. 2021a, A&A, 647, L2; Cernicharo et al. 2021b, A&A, 647, L3), start to allow us to quantify the abundant content of hydrocarbon rings in cold dark clouds and to identify the intermediate species that are probably behind the in situ bottom-up synthesis of arom. cycles in these environments. While c-C3HCCH is most likely formed through the reaction between the radical CCH and c-C3H2, the high obsd. abundances of cyclopentadiene and indene are difficult to explain through currently proposed chem. mechanisms. Further studies are needed to identify how five- and six-membered rings are formed under the cold conditions of a cloud such as TMC-1.
- 8Burkhardt, A. M.; Long Kelvin Lee, K.; Bryan Changala, P.; Shingledecker, C. N.; Cooke, I. R.; Loomis, R. A.; Wei, H.; Charnley, S. B.; Herbst, E.; McCarthy, M. C. Discovery of the Pure Polycyclic Aromatic Hydrocarbon Indene (c-C9H8) with GOTHAM Observations of TMC-1. Astrophys. J. Lett. 2021, 913 (2), L18, DOI: 10.3847/2041-8213/abfd3a8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsFWhsL7L&md5=a8e542ca35eb73e73d3d7dde4c38002fDiscovery of the pure polycyclic aromatic hydrocarbon indene (c-C9H8) with GOTHAM observations of TMC-1Burkhardt, Andrew M.; Lee, Kin Long Kelvin; Changala, P. Bryan; Shingledecker, Christopher N.; Cooke, Ilsa R.; Loomis, Ryan A.; Wei, Hongji; Charnley, Steven B.; Herbst, Eric; McCarthy, Michael C.; McGuire, Brett A.Astrophysical Journal, Letters (2021), 913 (2), L18CODEN: AJLEEY; ISSN:2041-8213. (IOP Publishing Ltd.)Polycyclic arom. hydrocarbons (PAHs) have long been invoked in the study of interstellar and protostellar sources, but the unambiguous identification of any individual PAH has proven elusive until very recently. As a result, the formation mechanisms for this important class of mols. remain poorly constrained. Here we report the first interstellar detection of a pure hydrocarbon PAH, indene (C9H8), as part of the GBT Observations of TMC-1: Hunting for Arom. Mols. (GOTHAM) survey. This detection provides a new avenue for chem. inquiry, complementing the existing detections of CN-functionalized arom. mols. From fitting the GOTHAM observations, indene is found to be the most abundant org. ring detected in TMC-1 to date. And from astrochem. modeling with nautilus, the obsd. abundance is greater than the model's prediction by several orders of magnitude, suggesting that current formation pathways in astrochem. models are incomplete. The detection of indene in relatively high abundance implies related species such as cyanoindene, cyclopentadiene, toluene, and styrene may be detectable in dark clouds.
- 9Kelvin Lee, K. L.; Changala, P. B.; Loomis, R. A.; Burkhardt, A. M.; Xue, C.; Cordiner, M. A.; Charnley, S. B.; McCarthy, M. C.; McGuire, B. A. Interstellar Detection of 2-Cyanocyclopentadiene, C5H5CN, a Second Five-Membered Ring toward TMC-1. Astrophys. J. Lett. 2021, 910 (1), L2, DOI: 10.3847/2041-8213/abe764There is no corresponding record for this reference.
- 10McCarthy, M. C.; Lee, K. L. K.; Loomis, R. A.; Burkhardt, A. M.; Shingledecker, C. N.; Charnley, S. B.; Cordiner, M. A.; Herbst, E.; Kalenskii, S.; Willis, E. R. Interstellar Detection of the Highly Polar Five-Membered Ring Cyanocyclopentadiene. Nat. Astron. 2021, 5 (2), 176– 180, DOI: 10.1038/s41550-020-01213-yThere is no corresponding record for this reference.
- 11Bézard, B.; Drossart, P.; Encrenaz, T.; Feuchtgruber, H. Benzene on the Giant Planets. Icarus 2001, 154 (2), 492– 500, DOI: 10.1006/icar.2001.671911https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XitlGnurc%253D&md5=030bee31a6dfe535c02b8aa2b974343eBenzene on the Giant PlanetsBezard, Bruno; Drossart, Pierre; Encrenaz, Therese; Feuchtgruber, HelmutIcarus (2001), 154 (2), 492-500CODEN: ICRSA5; ISSN:0019-1035. (Academic Press)We report the detection of benzene in the upper atmospheres of Jupiter at midlatitudes and Saturn (disk av.). Observations with the Short-Wavelength Spectrometer of the IR Space Observatory reveal emission from the Q-branch of benzene ∼14.84 μm on these 2 planets but not on Uranus and Neptune. Column densities were derived through radiative transfer calcns. assuming various mixing ratio profiles. The inferred abundances are 9+4.5-7.5 × 1014 mols. cm-2 above the 50-mbar level on Jupiter and 4.7+2.1-1.1 × 1013 mols. cm-2 above the 10-mbar level on Saturn. Upper limits were derived for Uranus and Neptune. Results are compared with existing chem. models. (c) 2001 Academic Press.
- 12Haythornthwaite, R. P.; Coates, A. J.; Jones, G. H.; Wellbrock, A.; Waite, J. H.; Vuitton, V.; Lavvas, P. Heavy Positive Ion Groups in Titan’s Ionosphere from Cassini Plasma Spectrometer IBS Observations. Planet. Sci. J. 2021, 2 (1), 26, DOI: 10.3847/PSJ/abd404There is no corresponding record for this reference.
- 13Waite, J. H.; Young, D. T.; Cravens, T. E.; Coates, A. J.; Crary, F. J.; Magee, B.; Westlake, J. Planetary Science: The Process of Tholin Formation in Titan’s Upper Atmosphere. Science (1979) 2007, 316 (5826), 870– 875, DOI: 10.1126/science.1139727There is no corresponding record for this reference.
- 14Pizzarello, S.; Shock, E. The Organic Composition of Carbonaceous Meteorites: The Evolutionary Story Ahead of Biochemistry. Cold Spring Harb Perspect Biol. 2010, 2 (3), a002105, DOI: 10.1101/cshperspect.a002105There is no corresponding record for this reference.
- 15Altwegg, K.; Balsiger, H.; Fuselier, S. A. Cometary Chemistry and the Origin of Icy Solar System Bodies: The View After Rosetta. Annu. Rev. Astron. Astrophys. 2019, 57 (1), 113– 155, DOI: 10.1146/annurev-astro-091918-10440915https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFenurnL&md5=16352cde4b478766ea25308d26c4f721Cometary Chemistry and the Origin of Icy Solar System Bodies: The View After RosettaAltwegg, Kathrin; Balsiger, Hans; Fuselier, Stephen A.Annual Review of Astronomy and Astrophysics (2019), 57 (), 113-155CODEN: ARAAAJ; ISSN:0066-4146. (Annual Reviews)In situ research of cometary chem. began when measurements from the Giotto mission at Comet 1P/Halley revealed the presence of complex orgs. in the coma. New telescopes and space missions have provided detailed remote and in situ measurements of the compn. of cometary volatiles. Recently, the Rosetta mission to Comet 67P/Churyumov-Gerasimenko (67P) more than doubled the no. of parent species and the no. of isotopic ratios known for comets. Forty of the 71 parent species have also been detected in pre- and protostellar clouds. Most isotopic ratios are nonsolar. This diverse origin is in contrast to that of the Sun, which received its material from the bulk of the collapsing cloud. The xenon isotopic ratios measured in 67P can explain the long-standing question about the origin of terrestrial atm. xenon. These findings strengthen the notion that comets are indeed an important link between the ISM and today's solar system including life on Earth. Nonsolar isotopic ratios for species such as Xe, N, S, and Si point to a nonhomogenized protoplanetary disk from which comets received their material. The similarity of the org. inventories of comets and presolar and protostellar material makes it plausible that this material was accreted almost unaltered by comets from the presolar stage. Large variations in the deuterium-to-hydrogen ratio in water for comets indicate a large range in the protoplanetary disk from which comets formed. The amt. of orgs. delivered by comets to Earth may be highly significant.
- 16Ali, A.; Sittler, E. C.; Chornay, D.; Rowe, B. R.; Puzzarini, C. Organic Chemistry in Titan’s Upper Atmosphere and Its Astrobiological Consequences: I. Views towards Cassini Plasma Spectrometer (CAPS) and Ion Neutral Mass Spectrometer (INMS) Experiments in Space. Planet. Space Sci. 2015, 109–110 (1), 46– 63, DOI: 10.1016/j.pss.2015.01.01516https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXislSltLo%253D&md5=3fa19a03b9baa1c77981037d0666eebaOrganic chemistry in Titan's upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in spaceAli, A.; Sittler, E. C.; Chornay, D.; Rowe, B. R.; Puzzarini, C.Planetary and Space Science (2015), 109-110 (), 46-63CODEN: PLSSAE; ISSN:0032-0633. (Elsevier Ltd.)The discovery of carbocations and carbanions by Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) instruments onboard the Cassini spacecraft in Titan's upper atm. is truly amazing for astrochemists and astrobiologists. In this paper we identify the reaction mechanisms for the growth of the complex macromols. obsd. by the CAPS Ion Beam Spectrometer (IBS) and Electron Spectrometer (ELS). This identification is based on a recently published paper which emphasizes the role of Olah's nonclassical carbonium ion chem. in the synthesis of the org. mols. obsd. in Titan's thermosphere and ionosphere by INMS. The main conclusion of that work was the demonstration of the presence of the cyclopropenyl cation - the simplest Huckel's arom. mol. - and its cyclic Me derivs. in Titan's atm. at high altitudes. In this study, we present the transition from simple arom. mols. to the complex ortho-bridged bi- and tri-cyclic hydrocarbons, e.g., CH+2 mono-substituted naphthalene and phenanthrene, as well as the ortho- and peri-bridged tri-cyclic arom. ring, e.g., perinaphthenyl cation. These rings could further grow into tetra-cyclic and the higher order ring polymers in Titan's upper atm. Contrary to the pre-Cassini observations, the nitrogen chem. of Titan's upper atm. is found to be extremely rich. A variety of N-contg. hydrocarbons including the N-heterocycles where a CH group in the polycyclic rings mentioned above is replaced by an N atom, e.g., CH+2 substituted deriv. of quinoline (benzopyridine), are found to be dominant in Titan's upper atm. The mechanisms for the formation of complex mol. anions are discussed as well. It is proposed that many closed-shell complex carbocations after their formation first, in Titan's upper atm., undergo the kinetics of electron recombination to form open-shell neutral radicals. These radical species subsequently might form carbanions via radiative electron attachment at low temps. with thermal electrons. The classic example is the perinaphthenyl anion in Titan's upper atm. Therefore, future astronomical observations of selected carbocations and corresponding carbanions are required to settle the key issue of mol. anion chem. on Titan. Other than earth, Titan is the only planetary body in our solar system that is known to have reservoirs of permanent liqs. on its surface. The synthesis of complex biomols. either by org. catalysis of pptd. solutes "on hydrocarbon solvent" on Titan or through the solvation process indeed started in its upper atm. The most notable examples in Titan's prebiotic atm. chem. are conjugated and arom. polycyclic mols., N-heterocycles including the presence of imino >C=N-H functional group in the carbonium chem. Our major conclusion in this paper is that the synthesis of org. compds. in Titan's upper atm. is a direct consequence of the chem. of carbocations involving the ion-mol. reactions. The observations of complexity in the org. chem. on Titan from the Cassini-Huygens mission clearly indicate that Titan is so far the only planetary object in our solar system that will most likely provide an answer to the question of the synthesis of complex biomols. on the primitive earth and the origin of life.
- 17Vuitton, V.; Yelle, R. V.; McEwan, M. J. Ion Chemistry and N-Containing Molecules in Titan’s Upper Atmosphere. Icarus 2007, 191 (2), 722– 742, DOI: 10.1016/j.icarus.2007.06.023There is no corresponding record for this reference.
- 18Anicich, V. G.; McEwan, M. J. Ion–Molecule Chemistry in Titan’s Ionosphere. Planet. Space Sci. 1997, 45 (8), 897– 921, DOI: 10.1016/S0032-0633(97)00053-618https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXmvFGgtbc%253D&md5=2dd5d04636c3f39ded03adb4502e1d34Ion-molecule chemistry in Titan's ionosphereAnicich, Vincent G.; Mcewan, Murray J.Planetary and Space Science (1997), 45 (8), 897-921CODEN: PLSSAE; ISSN:0032-0633. (Elsevier)A review with many refs. A summary is presented of the information available from lab. studies of ion-mol. reactions that is relevant to the chem. occurring in Titan's ionosphere. Reaction information from the literature has been collated and many new reactions have been measured, including some ion-atom reactions. The sequences of ion-neutral reactions can lead to a rapid increase in ion size. How this increase may lead to aerosol prodn. at the base of the ionosphere is briefly discussed. Lab. observations of extremely rapid termol. ion-neutral assocn. reactions indicate that these assocn. reactions are viable contributors to the ion chem. at the base of Titan's ionosphere.
- 19West, B.; Joblin, C.; Blanchet, V.; Bodi, A.; Sztáray, B.; Mayer, P. M. On the Dissociation of the Naphthalene Radical Cation: New IPEPICO and Tandem Mass Spectrometry Results. J. Phys. Chem. A 2012, 116 (45), 10999– 11007, DOI: 10.1021/jp309170519https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFClsLvE&md5=8b773c4bb6a4ac2b550d775730dae5eaOn the Dissociation of the Naphthalene Radical Cation: New iPEPICO and Tandem Mass Spectrometry ResultsWest, Brandi; Joblin, Christine; Blanchet, Valerie; Bodi, Andras; Sztaray, Balint; Mayer, Paul M.Journal of Physical Chemistry A (2012), 116 (45), 10999-11007CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)The dissocn. of the naphthalene radical cation was restudied here by a combination of tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C10H8•+ → C10H7+ + H (m/z = 127); (R2) C10H8•+ → C8H6•+ + C2H2 (m/z = 102); (R3) C10H8•+ → C6H6•+ + C4H2 (m/z = 78); (R4) C10H8•+ → C10H6•+ + H2 (m/z = 126); (R5) C10H7+ → C6H5+ + C4H2 (m/z = 77); (R6) C10H7+ → C10H6•+ + H (m/z = 126). The E0 activation energies for the reactions deduced from the present measurements are (in eV) 4.20 ± 0.04 (R1), 4.12 ± 0.05 (R2), 4.27 ± 0.07 (R3), 4.72 ± 0.06 (R4), 3.69 ± 0.26 (R5), and 3.20 ± 0.13 (R6). The corresponding entropies of activation, ΔS‡1000K, derived in the present study are (in J K-1 mol-1) 2 ± 2 (R1), 0 ± 2 (R2), 4 ± 4 (R3), 11 ± 4 (R4), 5 ± 15 (R5), and -19 ± 11 (R6). The derived E0 value, combined with the previously reported IE of naphthalene (8.1442 eV) results in an enthalpy of formation for the naphthyl cation, ΔfH°0K = 1148 ± 14 kJ mol-1/ΔfH°298K = 1123 ± 14 kJ mol-1 (site of dehydrogenation unspecified), slightly lower than the previous est. by Gotkis and co-workers. The derived E0 for the second H-loss leads to a ΔfH° for ion 7, the cycloprop[a]indene radical cation, of ΔfH°0K =1457 ± 27 kJ mol-1/ΔfH°298K(C10H6+) = 1432 ± 27 kJ mol-1. Detailed comparisons are provided with values (exptl. and theor.) available in the literature.
- 20Bouwman, J.; De Haas, A. J.; Oomens, J. Spectroscopic Evidence for the Formation of Pentalene+ in the Dissociative Ionization of Naphthalene. Chem. Commun. 2016, 52 (12), 2636– 2638, DOI: 10.1039/C5CC10090A20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjslemtQ%253D%253D&md5=358f1d8954f78741f1ec61c6dcb45a48Spectroscopic evidence for the formation of pentalene+ in the dissociative ionization of naphthaleneBouwman, Jordy; de Haas, Arjen J.; Oomens, JosChemical Communications (Cambridge, United Kingdom) (2016), 52 (12), 2636-2638CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Although acetylene loss is well known to constitute the main breakdown pathway of polycyclic arom. hydrocarbon (PAH) species, the mol. structure of the dissocn. products remains only poorly characterized. For instance, the structure of the C8H6 product ion formed upon acetylene loss from the smallest PAH naphthalene (C10H8) has not been exptl. established. Several C8H6+ isomers are conceivable, including phenylacetylene, benzocyclobutadiene, pentalene as well as a no. of acyclic products. Here we present IR spectroscopic evidence for the formation of the (anti-arom.) pentalene structure using a combination of tandem mass spectrometry and IR laser spectroscopy. The formation of pentalene is suggestive of facile 6- to 5-membered ring conversion, which possibly has implications for the PAH/fullerene interrelationship in energetic settings such as the interstellar medium and combustion environments.
- 21Panchagnula, S.; Bouwman, J.; Rap, D. B.; Castellanos, P.; Candian, A.; Mackie, C.; Banhatti, S.; Brünken, S.; Linnartz, H.; Tielens, A. G. G. M. Structural Investigation of Doubly-Dehydrogenated Pyrene Cations. Phys. Chem. Chem. Phys. 2020, 22, 21651, DOI: 10.1039/D0CP02272A21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB38jovFalsw%253D%253D&md5=8188f13b115a70796f9cc0fdd8308c72Structural investigation of doubly-dehydrogenated pyrene cationsPanchagnula Sanjana; Bouwman Jordy; Rap Daniel B; Castellanos Pablo; Candian Alessandra; Mackie Cameron; Banhatti Shreyak; Brunken Sandra; Linnartz Harold; Tielens Alexander G G MPhysical chemistry chemical physics : PCCP (2020), 22 (38), 21651-21663 ISSN:.The vibrationally resolved spectra of the pyrene cation and doubly-dehydrogenated pyrene cation (C16H10(+); Py(+) and C16H8(+); ddPy(+)) are presented. Infrared predissociation spectroscopy is employed to measure the vibrational spectrum of both species using a cryogenically cooled 22-pole ion trap. The spectrum of Py(+) allows a detailed comparison with harmonic and anharmonic density functional theory (DFT) calculated normal mode frequencies. The spectrum of ddPy(+) is dominated by absorption features from two isomers (4,5-ddPy(+) and 1,2-ddPy(+)) with, at most, minor contributions from other isomers. These findings can be extended to explore the release of hydrogen from interstellar PAH species. Our results suggest that this process favours the loss of adjacent hydrogen atoms.
- 22Lemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Willemsen, B.; Rijs, A. M. Polycyclic Aromatic Hydrocarbon Formation Chemistry in a Plasma Jet Revealed by IR-UV Action Spectroscopy. Nat. Commun. 2020, 11 (1), 269, DOI: 10.1038/s41467-019-14092-322https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXivFOgsbY%253D&md5=80b9778670e41e77740d8533b9a98168Polycyclic aromatic hydrocarbon formation chemistry in a plasma jet revealed by IR-UV action spectroscopyLemmens, Alexander K.; Rap, Daniel B.; Thunnissen, Johannes M. M.; Willemsen, Bryan; Rijs, Anouk M.Nature Communications (2020), 11 (1), 269CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Large polycyclic arom. hydrocarbons (PAHs) are the most abundant complex mols. in the interstellar medium; however, their possible formation pathways from small mol. species are still elusive. In the present work, we follow and characterize the formation of PAHs in an elec. discharge, specifically the PAH naphthalene in a mol. beam of argon. The fragments, products and reaction intermediates are unambiguously structurally identified by mass-selective IR-UV spectroscopy combined with quantum chem. calcns. This expt. provides evidence of the formation of larger PAHs contg. up to four cyclic rings in the gas phase originating from a non-radical PAH mol. as a precursor. In addn. to PAH formation, key resonance stabilized radical intermediates and intermediates contg. di-acetylenic side groups are unambiguously identified in our expt. We thereby not only reveal competing formation pathways to larger PAHs, but also identify intermediate species to PAH formation that are candidates for detection in radio-astronomy.
- 23Lee, K. L. K.; McCarthy, M. Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave Spectroscopy. J. Phys. Chem. Lett. 2019, 10 (10), 2408– 2413, DOI: 10.1021/acs.jpclett.9b0058623https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXot1yjsbk%253D&md5=f020b3e9ee45e5b17f2be2cf52e2e3c7Study of Benzene Fragmentation, Isomerization, and Growth Using Microwave SpectroscopyLee, Kin Long Kelvin; McCarthy, MichaelJournal of Physical Chemistry Letters (2019), 10 (10), 2408-2413CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Using a combination of broadband and cavity Fourier transform microwave spectroscopies, and newly developed anal. and assignment tools, the discharge products of benzene have been extensively studied in the 2-18 GHz frequency range. More than 450 spectral features with intensities greater than 6σ of the noise RMS were identified, of which of roughly four-fifths (82%) constituting 90% of the total spectral intensity were assigned to 38 species previously detected in the radio band, and nine entirely new hydrocarbon mols. were identified. The new species include both branched and chain fragments of benzene, high energy C6H6 isomers, and larger mols. such as phenyldiacetylene and isomers of fulvenallene; taken together they account for roughly half of the no. of obsd. transitions and 51% of the spectral line intensity. Transitions from vibrationally excited states of several mols. were also identified in the course of this investigation. A key aspect of the present anal. was implementation of a rapid and efficient workflow to assign spectral features from known mols. and to identify line progressions by pattern recognition techniques.
- 24McCarthy, M. C.; Lee, K. L. K.; Carroll, P. B.; Porterfield, J. P.; Changala, P. B.; Thorpe, J. H.; Stanton, J. F. Exhaustive Product Analysis of Three Benzene Discharges by Microwave Spectroscopy. J. Phys. Chem. A 2020, 124 (25), 5170– 5181, DOI: 10.1021/acs.jpca.0c0291924https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXpvVGqsL8%253D&md5=e97b9dbf3992cbc51a9dc6406154c5cbExhaustive Product Analysis of Three Benzene Discharges by Microwave SpectroscopyMcCarthy, Michael C.; Lee, Kin Long Kelvin; Carroll, P. Brandon; Porterfield, Jessica P.; Changala, P. Bryan; Thorpe, James H.; Stanton, John F.Journal of Physical Chemistry A (2020), 124 (25), 5170-5181CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)Using chirped and cavity microwave spectroscopies, automated double resonance, new high-speed fitting and deep learning algorithms, and large databases of computed structures, the discharge products of benzene alone, or in combination with mol. oxygen or nitrogen, have been exhaustively characterized between 6.5 and 26 GHz. In total, more than 3300 spectral features were obsd.; 89% of these, accounting for 97% of the total intensity, have now been assigned to 152 distinct chem. species and 60 of their variants (i.e., isotopic species and vibrationally excited states). Roughly 50 of the products are entirely new or poorly characterized at high resoln., including many heavier by mass than the precursor benzene. These findings provide direct evidence for a rich architecture of two- and three-dimensional carbon and indicate that benzene growth, particularly the formation of ring-chain mols., occurs facilely under our exptl. conditions. The present anal. also illustrates the utility of microwave spectroscopy as a precision tool for complex mixt. anal., irresp. of whether the rotational spectrum of a product species is known a priori or not. From this large quantity of data, for example, it is possible to det. with confidence the relative abundances of different product masses, but more importantly the relative abundances of different isomers with the same mass. The complementary nature of this type of anal. to traditional mass spectrometry is discussed.
- 25Roberts, G. M.; Williams, C. A.; Young, J. D.; Ullrich, S.; Paterson, M. J.; Stavros, V. G. Unraveling Ultrafast Dynamics in Photoexcited Aniline. J. Am. Chem. Soc. 2012, 134 (30), 12578– 12589, DOI: 10.1021/ja302972925https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XovFaks7o%253D&md5=62d18b1b7a3caeb954ab9956e320a449Unraveling Ultrafast Dynamics in Photoexcited AnilineRoberts, Gareth M.; Williams, Craig A.; Young, Jamie D.; Ullrich, Susanne; Paterson, Martin J.; Stavros, Vasilios G.Journal of the American Chemical Society (2012), 134 (30), 12578-12589CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A combination of ultrafast time-resolved velocity map imaging (TR-VMI) methods and complete active space SCF (CASSCF) ab initio calcns. are implemented to investigate the electronic excited-state dynamics in aniline (aminobenzene), with a perspective for simulation, physicochem., physicochem. 1πσ* mediated dynamics along the amino moiety in the purine derived DNA bases. This synergy between expt. and theory has enabled a comprehensive picture of the photochem. pathways/conical intersections (CIs), which govern the dynamics in aniline, to be established over a wide range of excitation wavelengths. TR-VMI studies following excitation to the lowest-lying 1ππ* state (11ππ*) with a broadband femtosecond laser radiation pulse, centered at wavelengths longer than 250 nm (4.97 eV), do not generate any measurable signature for 1πσ* driven N-H bond fission on the amino group. Between wavelengths of 250 and >240 nm (<5.17 eV), coupling from 11ππ* onto the 1πσ* state at a 11ππ*/1πσ* CI facilitates ultrafast nonadiabatic N-H bond fission through a 1πσ*/S0 CI in <1 silicon::polycryst.,, a notion supported by CASSCF results. For excitation to the higher lying 21ππ* state, calcns. reveal a near barrierless pathway for CI coupling between the 21ππ* and 11ππ* states, enabling the excited-state population to evolve through a rapid sequential 21ππ* → 11ππ* → 1πσ* → N-H fission mechanism, which we observe to take place in 155 ± 30 fs at 240 nm. We also postulate that an analogous cascade of CI couplings facilitates N-H bond scission along the 1πσ* state in 170 ± 20 fs, following 200 nm (6.21 eV) excitation to the 31ππ* surface. Particularly illuminating is the fact that a no. of the CASSCF calcd. CI geometries in aniline bear an exceptional resemblance with previously calcd. CIs and potential energy profiles along the amino moiety in guanine, strongly suggesting that the results here may act as an excellent grounding for better understanding 1πσ* driven dynamics in this ubiquitous genetic building block.
- 26King, G. A.; Oliver, T. A. A.; Ashfold, M. N. R. Dynamical Insights into π1σ* State Mediated Photodissociation of Aniline. J. Chem. Phys. 2010, 132 (21), 214307, DOI: 10.1063/1.342754426https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXntVSrsrg%253D&md5=02fe7132c96e50f63ba5e2ccc8fb8270Dynamical insights into 1πσ* state mediated photodissociation of anilineKing, Graeme A.; Oliver, Thomas A. A.; Ashfold, Michael N. R.Journal of Chemical Physics (2010), 132 (21), 214307/1-214307/12CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)This article reports a comprehensive study of the mechanisms of H atom loss in aniline (C6H5NH2) following UV excitation, using H (Rydberg) atom photofragment translational spectroscopy. N-H bond fission via the low lying 1πσ* electronic state of aniline is exptl. demonstrated. The 1πσ* potential energy surface (PES) of this prototypical arom. amine is essentially repulsive along the N-H stretch coordinate, but possesses a shallow potential well in the vertical Franck-Condon region, supporting quasibound vibrational levels. Photoexcitation at wavelengths (λphot) in the range 293.859 nm ≥ λphot ≥ 193.3 nm yields H atom loss via a range of mechanisms. With λphot resonant with the 11ππ*←S0 origin (293.859 nm), H atom loss proceeds via, predominantly, multiphoton excitation processes, resonantly enhanced at the one photon energy by the first 1ππ* excited state (the 11ππ* state). Direct excitation to the first few quasibound vibrational levels of the 1πσ* state (at wavelengths in the range 269.513 nm ≥ λphot ≥ 260 nm) induces N-H bond fission via H atom tunneling through an exit barrier into the repulsive region of the 1πσ* PES, forming anilino (C6H5NH) radical products in their ground electronic state, and with very limited vibrational excitation; the photo-prepd. vibrational mode in the 1πσ* state generally evolves adiabatically into the corresponding mode of the anilino radical upon dissocn. However, as the excitation wavelength is reduced (λphot < 260 nm), N-H bond fission yields fragments with substantially greater vibrational excitation, rationalized in terms of direct excitation to 11ππ* levels, followed by coupling to the 1πσ* PES via a 11ππ*/1πσ* conical intersection. Changes in product kinetic energy disposal once λphot approaches ∼ 230 nm likely indicate that the photodissocn. pathways of aniline proceed via direct excitation to the (higher) 21ππ* state. Anal. of the anilino fragment vibrational energy disposal-and thus the concomitant dynamics of 1πσ* state mediated photodissocn.-provides a particularly interesting study of competing σ*←π and π*←π absorption processes and develops our appreciation of the photochem. of arom. amines. It also allows revealing comparisons with simple amines (such as ammonia and methylamine) as well as the isoelectronic species, phenol. This study yields a value for the N-H bond strength in aniline, D0(H-anilino) = 31630 ± 40 cm-1. (c) 2010 American Institute of Physics.
- 27Roohi, H.; Moghadam, B. Decomposition Mechanism of the Phenylaminyl C6H5NH Radical to Propargyl and Acetylene: A M06-2X, CBS-QB3 and G4 Study. Chem. Phys. Lett. 2019, 730, 332– 339, DOI: 10.1016/j.cplett.2019.06.01827https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFyit7zP&md5=228cc69ac4862667a15aec1bbd25b205Decomposition mechanism of the phenylaminyl C6H5N·H radical to propargyl and acetylene: A M06-2X, CBS-QB3 and G4 studyRoohi, Hossein; Moghadam, BehnazChemical Physics Letters (2019), 730 (), 332-339CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)In this work, decompn. mechanism of the phenylaminyl radical C6H5N·H was investigated by means of M062X, G4 and CBS-QB3 methods. It is found that the energy barrier for conversion of most stable N-centered radical to less stable C-centered radicals is greater than the decompn. reaction. Two resonantly stabilized radicals propargyl and cyclopentadienyl were found on the potential energy surface of reaction. It is estd. that activation energy for sigmatropic H transfer rearrangement of cyclopentadienyl radical is 59.50 and 56.26 kcal/mol at G4 and M06-2X/6-311++G(d,p) levels, resp. The ΔH°f,g and ΔG°f,g values of all the radicals were calcd.
- 28Kühlewind, H.; Neusser, H. J.; Schlag, E. W. Multiphoton Metastable Ion Spectra and Ion Dissociation Kinetics: Analysis of the Decay Channels of the Aniline Cation with a Reflectron Time-of-Flight Instrument. J. Chem. Phys. 1985, 82 (12), 5452– 5456, DOI: 10.1063/1.44857928https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXlslOrsLw%253D&md5=ecc0790fec73c7cad28b66de0e7ae4c3Multiphoton metastable ion spectra and ion dissociation kinetics: analysis of the decay channels of the aniline cation with a reflectron time-of-flight instrumentKuehlewind, H.; Neusser, H. J.; Schlag, E. W.Journal of Chemical Physics (1985), 82 (12), 5452-6CODEN: JCPSA6; ISSN:0021-9606.Multiphoton mass spectrometry when carried out in conjunction with a reflecting field time-of-flight mass spectrometer yields rich new metastable ion spectra of polyat. mols., here aniline. The reflecting field acting also as an energy analyzer is particularly suitable for sensitive metastable ion detection without interference from stable fragment ions. With this technique several new metastable ion decay channels of the aniline cation have been obsd. On the basis of the measured metastable ion spectrum a reasonable fragmentation pathway for the aniline cation C6H7N+ after multiphoton excitation is presented. The prominent intensity of the metastable ion peak C5H6+ points to a narrow energy distribution within the aniline cation typical for a ladder switching multiphoton excitation mechanism.
- 29Geng, L.; Zhang, H.; Wu, H.; Sun, Z.; Luo, Z. Ionization and Dissociation of Benzene and Aniline under Deep Ultraviolet Laser Irradiation. Chin. J. Chem. Phys. 2020, 33 (5), 583– 589, DOI: 10.1063/1674-0068/cjcp200608629https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitlCmu7fI&md5=ec3291627cf9b23663668caad92ffa4fIonization and dissociation of benzene and aniline under deep ultraviolet laser irradiationGeng, Lijun; Zhang, Hanyu; Wu, Haiming; Sun, Zhendong; Luo, ZhixunChinese Journal of Chemical Physics (2020), 33 (5), 583-589CODEN: CJCPA6; ISSN:1674-0068. (American Institute of Physics)We report a study on photo-ionization of benzene and aniline with incidental subsequent dissocn. by the customized reflection time-of-flight mass spectrometer utilizing a deep UV 177.3 nm laser. Highly efficient ionization of benzene is obsd. with a weak C4H3+ fragment formed by undergoing disproportional C-C bond dissocn. In comparison, a major C5H6+· fragment and a minor C6H6+· radical are produced in the ionization of aniline pertaining to the removal of CNH· and NH· radicals, resp. First-principles calcn. is employed to reveal the photo-dissocn. pathways of these two mols. having a structural difference of just an amino group. It is demonstrated that hydrogen atom transfer plays an important role in the cleavage of C-C or C-N bonds in benzene and aniline ions. This study is helpful to understand the underlying mechanisms of chem. bond fracture of benzene ring and related arom. mols. (c) 2020 American Institute of Physics.
- 30Choe, J. C.; Cheong, N. R.; Park, S. M. Unimolecular Dissociation of Aniline Molecular Ion: A Theoretical Study. Int. J. Mass Spectrom. 2009, 279 (1), 25– 31, DOI: 10.1016/j.ijms.2008.09.01330https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVCgsbvF&md5=f2de6768b1f47e62718a63fab73cbc13Unimolecular dissociation of aniline molecular ion: A theoretical studyChoe, Joong Chul; Cheong, Nu Ri; Park, Seung MinInternational Journal of Mass Spectrometry (2009), 279 (1), 25-31CODEN: IMSPF8; ISSN:1387-3806. (Elsevier B.V.)The potential energy surface (PES) for dissocn. of aniline ion was detd. using d. functional theory MO calcns. at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. On the basis of the PES obtained, kinetic anal. was performed by Rice-Ramsperger-Kassel-Marcus (RRKM) calcns. The RRKM dissocn. rate consts. agreed well with previous exptl. data. The most favorable channel was formation of the cyclopentadiene ion by loss of HNC, occurring through consecutive ring opening and re-closure to a five-membered ring. Loss of H· could compete with the HNC loss at high energy, which occurred by direct cleavage of an N-H bond or through ring expansion.
- 31Jusko, P.; Brünken, S.; Asvany, O.; Thorwirth, S.; Stoffels, A.; Van Der Meer, L.; Berden, G.; Redlich, B.; Oomens, J.; Schlemmer, S. The FELion Cryogenic Ion Trap Beam Line at the FELIX Free-Electron Laser Laboratory: Infrared Signatures of Primary Alcohol Cations. Faraday Discuss. 2019, 217, 172– 202, DOI: 10.1039/C8FD00225H31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXovFGktro%253D&md5=6b35e401a6040a672b855a985df71712The FELion cryogenic ion trap beam line at the FELIX free-electron laser laboratory: infrared signatures of primary alcohol cationsJusko, Pavol; Bruenken, Sandra; Asvany, Oskar; Thorwirth, Sven; Stoffels, Alexander; van der Meer, Lex; Berden, Giel; Redlich, Britta; Oomens, Jos; Schlemmer, StephanFaraday Discussions (2019), 217 (Advances in Ion Spectroscopy), 172-202CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)The combination of a 4 K 22-pole ion trap instrument, FELion, with the widely tunable free electron lasers at the FELIX Lab. is described in detail. It allows for wide-range IR vibrational spectroscopy of mol. ions. In this study, the app. is used for IR vibrational predissocn. (IR-PD) measurements of the simple alc. cations of methanol and ethanol as well as their protonated forms. Spectra are taken by tagging the cold mol. ions with He atoms. The IR spectrum of protonated methanol is recorded for the first time, and the wavelength coverage for all other species is substantially extended. The bands of all spectra are analyzed by comparison to ab initio calcn. results at different levels of theory. Vibrational bands of different isomers and conformers (rotamers) are discussed and identified in the exptl. spectra. Besides the measurement of IR-PD spectra, the method of IR multiple photon dissocn. IR-MPD is applied for some cases. Spectral narrowing due to the cold environment is obsd. and rotational band contours are simulated. This will help in identifying more complex species using the IR-MPD method in future measurements. Overall the IR-PD spectra reveal more bands than are obsd. for the IR-MPD spectra. In particular, many new bands are obsd. in the fingerprint region. Depletion satn. of the finite no. of trapped ions is obsd. for the IR-PD spectra of the ethanol cation and the presence of only one isomeric species is concluded. This special feature of ion trapping spectroscopy may be used in future studies for addressing specific isomers or cleaning the ion cloud from specific isomers or conformers. In addn., the results of this study can be used as a basis to obtain high-resoln. IR vibrational and THz rotational spectra of alc. ions in order to detect them in space.
- 32Oepts, D.; van der Meer, A. F. G.; van Amersfoort, P. W. The Free-Electron-Laser User Facility FELIX. Infrared Phys. Technol. 1995, 36 (1), 297– 308, DOI: 10.1016/1350-4495(94)00074-U32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXltlCksrg%253D&md5=45dfdce37069160f5527f00358a50e58The free-electron-laser user facility FELIXOepts, D.; van der Meer, A. F. G.; van Amersfoort, P. W.Infrared Physics & Technology (1995), 36 (1), 297-308CODEN: IPTEEY; ISSN:1350-4495.The Free Electron Laser for IR expts. FELIX presents to its users a versatile source of radiation in the IR and far-IR spectral regions. Presently, the wavelength range of operation extends 5-110 μm (2000-90 cm-1). The wavelength is continuously tunable over an octave in a few minutes. The output normally consists of macropulses of 5-10 μs duration, formed by a train of micropulses of a few ps length. Av. power in the macropulses is of order 10 kW, peak power in the micropulses is in the MW range. The temporal and spectral characteristics of the micropulses can be controlled by varying the synchronism between the electron pulses and the optical pulses circulating in the laser cavity. Transform-limited pulse lengths of 2-20 ps can be generated. Long-range coherence was induced by phase-locking successive micropulses, and narrow-band, essentially single-mode, radiation was selected from the output.
- 33Zeh, D.; Bast, M.; Rap, D. B.; Schmid, P. C.; Thorwirth, S.; Brünken, S.; Schlemmer, S.; Schäfer, M. Cryogenic Messenger-IR Ion Spectroscopy Study of Phenol & Aniline Molecular Ions and of the Common Fragment Ion [C5H6] •+ Formed by EI-MS. J. Mol. Spectrosc. 2021, 378, 111453, DOI: 10.1016/j.jms.2021.11145333https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtVSgsrvI&md5=bf7f6ab8ea2321dfc3c552283da3bbe1Cryogenic Messenger-IR Ion Spectroscopy Study of Phenol & Aniline Molecular Ions and of the common Fragment Ion [C5H6]·+ formed by EI-MSZeh, Dennis; Bast, Marcel; Rap, Daniel B.; Schmid, Philipp C.; Thorwirth, Sven; Bruenken, Sandra; Schlemmer, Stephan; Schaefer, MathiasJournal of Molecular Spectroscopy (2021), 378 (), 111453CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Mol. ions of phenol and aniline as well as the fragment ion at m/z 66 formed by electron ionization are examd. with cryogenic messenger-IR ion spectroscopy and theory. According to the recorded IR spectra arom. ground state mol. ions of phenol and aniline are clearly identified. Similar to earlier reports our new set of spectroscopic and computational results supports the assumption that tautomeric mol. ions of phenol and aniline are only short-lived intermediates in the reaction path to the ultimate CO loss reaction product of phenol as well as the HNC loss product of aniline. Even the present cryogenic messenger-IR ion spectroscopy approach failed to collect spectroscopic evidence of the intermediate presence of these elusive tautomers of phenol and aniline mol. ions. However, our study clearly shows that the electron ionization mass spectrometry dissocn. product ion of phenol and aniline at m/z 66 is the cyclopentadiene radical cation [C5H6]·+ for the presence of which convincing spectroscopic evidence could be collected proving the structure assignment and identification. All messenger-IR ion spectroscopy expts. were conducted on a cryogenic 22-pole ion trap with the use of neon atoms for tagging. The MS instrument was coupled to a free electron laser delivering wavelength tunable IR radiation for spectroscopy. Harmonic and anharmonic force field calcns. complement the expts. and support band assignments of the recorded IR spectra and general data interpretation.
- 34Jusko, P.; Simon, A.; Wenzel, G.; Brünken, S.; Schlemmer, S.; Joblin, C. Identification of the Fragment of the 1-Methylpyrene Cation by Mid-IR Spectroscopy. Chem. Phys. Lett. 2018, 698, 206– 210, DOI: 10.1016/j.cplett.2018.03.02834https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXltlWisrc%253D&md5=590c47b7e54525dcfe7a303739d927fcIdentification of the fragment of the 1-methylpyrene cation by mid-IR spectroscopyJusko, Pavol; Simon, Aude; Wenzel, Gabi; Brunken, Sandra; Schlemmer, Stephan; Joblin, ChristineChemical Physics Letters (2018), 698 (), 206-210CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)The fragment of the 1-methylpyrene cation, C17H+11, is expected to exist in two isomeric forms, 1-pyrenemethylium PyrCH+2 and the tropylium contg. species PyrC+7. We measured the IR action spectrum of cold C17H+11 tagged with Ne using a cryogenic ion trap instrument coupled to the FELIX laser. Comparison of the exptl. data with d. functional theory calcns. allows us to identify the PyrCH+2 isomer in our expts. The IR Multi-Photon Dissocn. spectrum was also recorded following the C2H2 loss channel. Its anal. suggests combined effects of anharmonicity and isomerisation while heating the trapped ions, as shown by mol. dynamics simulations.
- 35Gerlich, D. Inhomogeneous RF Fields: A Versatile Tool for the Study of Processes with Slow Ions. In Advances in Chemical Physics: State-Selected and State-To-State Ion-Molecule Reaction Dynamics, Part 1. Experiment; Wiley, 1992; Vol. 82; DOI: 10.1002/9780470141397.ch1 .There is no corresponding record for this reference.
- 36Rap, D. B.; Marimuthu, A. N.; Redlich, B.; Brünken, S. Stable Isomeric Structures of the Pyridine Cation (C5H5N•+) and Protonated Pyridine (C5H5NH+) Elucidated by Cold Ion Infrared Spectroscopy. J. Mol. Spectrosc. 2020, 373, 111357, DOI: 10.1016/j.jms.2020.11135736https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvVOmurfO&md5=d5142ab80b6626f6573dc57116cc358eStable isomeric structures of the pyridine cation (C5H5N+) and protonated pyridine (C5H5NH+) elucidated by cold ion infrared spectroscopyRap, Daniel B.; Marimuthu, Aravindh N.; Redlich, Britta; Bruenken, SandraJournal of Molecular Spectroscopy (2020), 373 (), 111357CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Cold ion action spectroscopy is applied to record the gas phase IR fingerprint spectra of mass-selected C5H5N•+ and C5H5NH+ cations using an IR free electron laser. The structures of the cations are deduced from the exptl. spectra using anharmonic vibrational frequencies from d. functional theory calcns. A very good agreement between exptl. and theor. IR frequencies is obsd. The dominant structure of the C5H5N•+ cation is assigned to the arom. pyridine radical cation form. Addnl., a minor contribution of the lower energetic α-distonic isomer is obsd. The C5H5NH+ cation is ascribed to the arom. pyridinium cation where protonation has taken place on the nitrogen atom. The rare-gas tag used in the action spectroscopic method has a negligible effect on the vibrational frequencies. The obsd. species, with now accurately detd. vibrational frequencies, are good candidates for future rotational spectroscopic studies and IR observations in astronomical sources such as interstellar clouds or Titan's atm.
- 37Marimuthu, A. N.; Sundelin, D.; Thorwirth, S.; Redlich, B.; Geppert, W. D.; Brünken, S. Laboratory Gas-Phase Vibrational Spectra of [C3H3]+ Isomers and Isotopologues by IRPD Spectroscopy. J. Mol. Spectrosc. 2020, 374, 111377, DOI: 10.1016/j.jms.2020.11137737https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFegt7nN&md5=8cacaaa9e70f7ddbe83a2afcae58c37eLaboratory gas-phase vibrational spectra of [C3H3]+ isomers and isotopologues by IRPD spectroscopyMarimuthu, Aravindh N.; Sundelin, David; Thorwirth, Sven; Redlich, Britta; Geppert, Wolf D.; Brunken, SandraJournal of Molecular Spectroscopy (2020), 374 (), 111377CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)Gas phase vibrational spectra of [C3H3]+ isomers and their fully deuterated isotopologues measured in a cryogenic 22-pole ion trap are presented. The widely tunable free electron laser for IR expts., FELIX, was employed to cover the frequency range 500-2400 cm-1, complemented with an OPO/OPA system covering 2800-3400 cm-1. Spectral assignments for both the linear and cyclic isomeric form (H2C3H+ and c-C3H+3, resp.) are made based on various high-level computational studies. The effect of ion source conditions and different precursors (allene and propargyl chloride) for the preferential prodn. of a specific isomer is discussed. The perturbation of the vibrational band position due to complexation with neon in the recorded IR-predissocn. (IRPD) spectra are also reported in this study.
- 38Marimuthu, A. N.; Huis in’t Veld, F.; Thorwirth, S.; Redlich, B.; Brünken, S. Infrared Predissociation Spectroscopy of Protonated Methyl Cyanide, CH3CNH+. J. Mol. Spectrosc. 2021, 379, 111477, DOI: 10.1016/j.jms.2021.11147738https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXht1ehu7vJ&md5=72205daa46b9bf1f2ac4e5b184d96af9Infrared predissociation spectroscopy of protonated methyl cyanide, CH3CNH+Marimuthu, Aravindh N.; Huis in't Veld, Frank; Thorwirth, Sven; Redlich, Britta; Brunken, SandraJournal of Molecular Spectroscopy (2021), 379 (), 111477CODEN: JMOSA3; ISSN:0022-2852. (Elsevier B.V.)The gas phase vibrational spectrum of CH3CNH+ is investigated using a messenger IR predissocn. (IRPD) action spectroscopic method. Vibrational bands were recorded in the 300-1700 cm-1 and 2000-3300 cm-1 regions making use of the widely tunable free electron laser for IR expts., FELIX, coupled to a cryogenic ion trap instrument. Band assignments were aided by high-level quantum-chem. calcns., which showed excellent agreement with the exptl. data. Effects of the neon atom used as messenger in the IRPD method are investigated in detail. The data presented here will support astronomical searches for the CH3CNH+ ion in space, and provide a basis for high-resoln. ro-vibrational and pure rotational studies in vibrationally excited states.
- 39Brünken, S.; Lipparini, F.; Stoffels, A.; Jusko, P.; Redlich, B.; Gauss, J.; Schlemmer, S. Gas-Phase Vibrational Spectroscopy of the Hydrocarbon Cations l-C3H+, HC3H+, and c-C3H2+: Structures, Isomers, and the Influence of Ne-Tagging. J. Phys. Chem. A 2019, 123 (37), 8053– 8062, DOI: 10.1021/acs.jpca.9b0617639https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsF2ntL3P&md5=df5eb88bca69c7505159374a0a642371Gas-Phase Vibrational Spectroscopy of the Hydrocarbon Cations l-C3H+, HC3H+, and c-C3H2+: Structures, Isomers, and the Influence of Ne-TaggingBruenken, Sandra; Lipparini, Filippo; Stoffels, Alexander; Jusko, Pavol; Redlich, Britta; Gauss, Juergen; Schlemmer, StephanJournal of Physical Chemistry A (2019), 123 (37), 8053-8062CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)We report the first gas-phase vibrational spectra of the hydrocarbon ions C3H+ and C3H2+. The ions were produced by electron impact ionization of allene. Vibrational spectra of the mass-selected ions tagged with Ne were recorded using IR predissocn. spectroscopy in a cryogenic ion trap instrument using the intense and widely tunable radiation of a free electron laser. Comparison of high-level quantum chem. calcns. and resonant depletion measurements revealed that the C3H+ ion is exclusively formed in its most stable linear isomeric form, whereas two isomers were obsd. for C3H2+. Bands of the energetically favored cyclic c-C3H2+ are in excellent agreement with calcd. anharmonic frequencies, whereas for the linear open-shell HCCCH+ (2Πg) a detailed theor. description of the spectrum remains challenging because of Renner-Teller and spin-orbit interactions. Good agreement between theory and expt., however, is obsd. for the frequencies of the stretching modes for which an anharmonic treatment was possible. In the case of linear l-C3H+, small but non-negligible effects of the attached Ne on the ion fundamental band positions and the overall spectrum were found.
- 40Jusko, P.; Simon, A.; Banhatti, S.; Brünken, S.; Joblin, C. Direct Evidence of the Benzylium and Tropylium Cations as the Two Long-Lived Isomers of C7H7+. ChemPhysChem 2018, 19 (23), 3182– 3185, DOI: 10.1002/cphc.20180074440https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFSrtLnO&md5=97dde1e9510d450c52293bbfe0595953Direct Evidence of the Benzylium and Tropylium Cations as the Two Long-Lived Isomers of C7H7+Jusko, Pavol; Simon, Aude; Banhatti, Shreyak; Bruenken, Sandra; Joblin, ChristineChemPhysChem (2018), 19 (23), 3182-3185CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Disentangling the isomeric structure of C7H7+ is a longstanding exptl. issue. We report here the full mid-IR vibrational spectrum of C7H7+ tagged with Ne obtained with IR-predissocn. spectroscopy at 10 K. Satn. depletion measurements were used to assign the contribution of benzylium and tropylium isomers and demonstrate that no other isomer is involved. Recorded spectral features compare well with d. functional theory calcns. This opens perspectives for a better understanding and control of the formation paths leading to either tropylium or benzylium ions.
- 41Frisch, M. J. G.; Trucks, W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Gaussian 16 , Rev. A.03; 2016.There is no corresponding record for this reference.
- 42Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98 (7), 5648– 5652, DOI: 10.1063/1.46491342https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXisVWgtrw%253D&md5=291bbfc119095338bb1624f0c21c7ca8Density-functional thermochemistry. III. The role of exact exchangeBecke, Axel D.Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.
- 43Barone, V.; Cimino, P.; Stendardo, E. Development and Validation of the B3LYP/N07D Computational Model for Structural Parameter and Magnetic Tensors of Large Free Radicals. J. Chem. Theory Comput. 2008, 4 (5), 751– 764, DOI: 10.1021/ct800034c43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXksVShtb0%253D&md5=deffc27472a7b65a612cea495fe022b8Development and Validation of the B3LYP/N07D Computational Model for Structural Parameter and Magnetic Tensors of Large Free RadicalsBarone, Vincenzo; Cimino, Paola; Stendardo, EmilianoJournal of Chemical Theory and Computation (2008), 4 (5), 751-764CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Extensive calcns. on a large set of free radicals contg. atoms of the second and third row show that the B3LYP/N07D computational model provides remarkably accurate structural parameters and magnetic tensors at reasonable computational costs. The key of this success is the optimization of core-valence s functions for hyperfine coupling consts., while retaining (and even improving) the good performances of the parent 6-31 + G(d,p) basis set for valence properties through reoptimization of polarization and diffuse p functions.
- 44Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132 (15), 154104, DOI: 10.1063/1.338234444https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXkvVyks7o%253D&md5=2bca89d904579d5565537a0820dc2ae8A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-PuGrimme, Stefan; Antony, Jens; Ehrlich, Stephan; Krieg, HelgeJournal of Chemical Physics (2010), 132 (15), 154104/1-154104/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The method of dispersion correction as an add-on to std. Kohn-Sham d. functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coeffs. and cutoff radii that are both computed from first principles. The coeffs. for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos. (CN). They are used to interpolate between dispersion coeffs. of atoms in different chem. environments. The method only requires adjustment of two global parameters for each d. functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of at. forces. Three-body nonadditivity terms are considered. The method has been assessed on std. benchmark sets for inter- and intramol. noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean abs. deviations for the S22 benchmark set of noncovalent interactions for 11 std. d. functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs. also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. (c) 2010 American Institute of Physics.
- 45Puzzarini, C.; Biczysko, M.; Barone, V. Accurate Harmonic/Anharmonic Vibrational Frequencies for Open-Shell Systems: Performances of the B3LYP/N07D Model for Semirigid Free Radicals Benchmarked by CCSD(T) Computations. J. Chem. Theory Comput. 2010, 6 (3), 828– 838, DOI: 10.1021/ct900594h45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFams7Y%253D&md5=6d985f98f3c56b2b28bffdce5d8a5d48Accurate Harmonic/Anharmonic Vibrational Frequencies for Open-Shell Systems: Performances of the B3LYP/N07D Model for Semirigid Free Radicals Benchmarked by CCSD(T) ComputationsPuzzarini, Cristina; Biczysko, Malgorzata; Barone, VincenzoJournal of Chemical Theory and Computation (2010), 6 (3), 828-838CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Impressive growth of computer facilities and effective implementation of very accurate quantum mech. methods allow, nowadays, the detn. of structures and vibrational characteristics for small- to medium-sized mols. to a very high accuracy. Since the situation is much less clear for open-shell species, we decided to build a suitable database of harmonic and anharmonic frequencies for small-sized free radicals contg. atoms of the first two rows of the periodic table. The level of theory employed is the CCSD(T) model in conjunction with triple- and quadruple-ζ basis sets, whose accuracy has been checked with respect to the available exptl. data and/or converged quantum mech. computations. Next, in view of studies of larger open-shell systems, we have validated the B3LYP/N07D model with ref. to the above database: our results confirm previous suggestions about the remarkable reliability and reduced computational cost of this computational method. A no. of test computations show that basis set extension has negligible effects and other d. functionals (including last generation ones) deliver significantly worse results. Increased accuracy can be obtained, instead, by using CCSD(T) harmonic frequencies and B3LYP/N07D anharmonic corrections.
- 46Lemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Mackie, C. J.; Candian, A.; Tielens, A. G. G. M.; Rijs, A. M.; Buma, W. J. Anharmonicity in the Mid-Infrared Spectra of Polycyclic Aromatic Hydrocarbons: Molecular Beam Spectroscopy and Calculations. Astron. Astrophys. 2019, 628, A130, DOI: 10.1051/0004-6361/20193563146https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlOktbbJ&md5=54aa808993d11e69b7deba5abb1a1582Anharmonicity in the mid-infrared spectra of polycyclic aromatic hydrocarbons: molecular beam spectroscopy and calculationsLemmens, A. K.; Rap, D. B.; Thunnissen, J. M. M.; Mackie, C. J.; Candian, A.; Tielens, A. G. G. M.; Rijs, A. M.; Buma, W. J.Astronomy & Astrophysics (2019), 628 (), A130CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)Aims. In this work we det. the effects of anharmonicity on the mid-IR spectra of the linear polycyclic arom. hydrocarbons (PAHs) naphthalene, anthracene, tetracene and pentacene recorded using the free electron laser FELIX. Methods. Comparison of exptl. spectra obtained under supersonic jet conditions with theor. predicted spectra was used to show if anharmonicity explicitly needs to be taken into account. Results. Anharmonic spectra obtained using second-order vibrational perturbation theory agree on av. within 0.5% of the exptl. frequencies. Importantly, they confirm the presence of combination bands with appreciable intensity in the 5-6μm region. These combination bands contain a significant fraction of the IR absorption, which scales linearly with the size of the PAH. Detection and assignment of the combination bands are a preliminary indication of the accuracy of far-IR modes in our anharmonic theor. spectra. Detailed anal. of the periphery-sensitive CH out-of-plane band of naphthalene reveals that there is still room for improvement of the VPT2 approach. In addn., the implications of our findings for the anal. of the arom. IR bands are discussed.
- 47Montgomery, J. A.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A. A Complete Basis Set Model Chemistry. VII. Use of the Minimum Population Localization Method. J. Chem. Phys. 2000, 112 (15), 6532– 6542, DOI: 10.1063/1.48122447https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitlSrsLc%253D&md5=af2e5c3f4d631ec7c98897040736828bA complete basis set model chemistry. VII. Use of the minimum population localization methodMontgomery, J. A., Jr.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A.Journal of Chemical Physics (2000), 112 (15), 6532-6542CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)It is shown that localization is necessary to preserve size consistency in nonlinear extrapolations of mol. energies. We demonstrate that the unphys. behavior of Mulliken populations obtained from extended basis set wave functions can lead to incomplete localization of orbitals by the Pipek-Mezey population localization method, and introduce a modification to correct this problem. The new localization procedure, called min. population localization, is incorporated into the CBS-QB3 and the new CBS-4M model chemistries, and their performance is assessed on the G2/97 test set. The errors found for CBS-QB3 are comparable with those for the G3 and G3(MP2) (mean abs. deviation of 1.10, 0.94, and 1.21 kcal/mol, resp., on the G2/97 test set). The CBS-4M is less accurate than the other models (mean abs. deviation of 3.26 kcal/mol on the G2/97 test set), but can be applied to much larger systems. The modified localization method resolves several problem cases found with CBS-4 and improves the reliability of CBS-QB3.
- 48Montgomery, J. A.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A. A Complete Basis Set Model Chemistry. VI. Use of Density Functional Geometries and Frequencies. J. Chem. Phys. 1999, 110 (2–12), 2822– 2827, DOI: 10.1063/1.47792448https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXltlKntg%253D%253D&md5=f5da251681f5c1ba20c7268b98152415A complete basis set model chemistry. VI. Use of density functional geometries and frequenciesMontgomery, J. A., Jr.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A.Journal of Chemical Physics (1999), 110 (6), 2822-2827CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The recently introduced complete basis set, CBS-Q, model chem. is modified to use B3LYP hybrid d. functional geometries and frequencies, which give both improved reliability (max. error for the G2 test set reduced from 3.9 to 2.8 kcal/mol) and increased accuracy (mean abs. error reduced from 0.98 to 0.87 kcal/mol), with little penalty in computational speed. The use of a common method for geometries and frequencies makes the modified model applicable to transition states for chem. reactions.
- 49Smith, M. A.; Hager, J. W.; Wallace, S. C. Two Color Photoionization Spectroscopy of Jet Cooled Aniline: Vibrational Frequencies of the Aniline X̃2B1 Radical Cation. J. Chem. Phys. 1984, 80 (7), 3097– 3105, DOI: 10.1063/1.44712449https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXitVSgsbg%253D&md5=70d0007df53e24b4c042161aff182cb5Two color photoionization spectroscopy of jet cooled aniline: vibrational frequencies of the aniline ~X2B1 radical cationSmith, Mark A.; Hager, James W.; Wallace, Stephen C.Journal of Chemical Physics (1984), 80 (7), 3097-105CODEN: JCPSA6; ISSN:0021-9606.Photoionization-efficiency spectra of free jet expansion cooled aniline in the 1B2 excited state were obtained by the technique of 2-color photoionization spectroscopy. The adiabatic ionization potential of rotationally cooled (<5 K) aniline is 62 265 ± 18 cm-1. By pumping a variety of vibronic transitions, photoionization-efficiency curves were obtained from discrete vibrational levels in the 1B2 state. The spectra generally show a strong propensity for vertical (Δv = 0) ionization. As a result, it was possible to det. the vibrational frequencies of the ground state aniline 2B1 radical cation with good precision for 6 vibrational modes. Vibrational progressions obsd. in the threshold curves support these assignments as well as allowing the observation of 2 addnl. modes in the ion which do not manifest themselves in the ‾A(1B2) ← ‾X(1A1) electronic spectrum. The magnitude of these vibrational frequencies compared to those known for the ground and 1st excited state of aniline suggest that the 2B1 ionic state is more rigidly planar than the 1B2 excited state.
- 50Lifshitz, C.; Malinovich, Y. Time Resolved Photoionization Mass Spectrometry in the Millisecond Range. Int. J. mass Spectrom. Ion Processes 1984, 60 (1), 99– 105, DOI: 10.1016/0168-1176(84)80078-650https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXlvVSrtr8%253D&md5=f2e285cf0ca26fe764d1a159a5d5064aTime resolved photoionization mass spectrometry in the millisecond rangeLifshitz, C.; Malinovich, Y.International Journal of Mass Spectrometry and Ion Processes (1984), 60 (), 99-105CODEN: IJMPDN; ISSN:0168-1176.A photoionization mass spectrometer operating in a time resolved manner, from the microsecond to the millisecond range, was constructed. A Hinteregger vacuum-UV light source is pulsed and the photoions produced are trapped in a cylindrical ion trap. Time resolved ionization efficiency curves are obtained. Several mols. which demonstrate large kinetic shifts were studied. Dissocn. rate coeffs. of ∼1 s-1 or lower were obsd. by using extended signal averaging techniques.
- 51Zaretskii, Z. V. I.; Oren, D.; Kelner, L. Automatic Method for the Measurement of the Electron Impact Ionization and Appearance Potentials. Appl. Spectrosc. 1976, 30 (3), 366– 368, DOI: 10.1366/00037027677445727251https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE28XkslOjtro%253D&md5=5f07e2e9b0e1674c7792217fce0ebbceAutomatic method for the measurement of the electron impact ionization and appearance potentialsZaretskii, Ze'ev V. I.; Oren, David; Kelner, LeonidApplied Spectroscopy (1976), 30 (3), 366-8CODEN: APSPA4; ISSN:0003-7028.An automatic electronic scanner for the rapid recording of ionization efficiency curves was described.
- 52Lifshitz, C.; Gotchiguian, P.; Roller, R. Time-Dependent Mass Spectra and Breakdown Graphs. The Kinetic Shift in Aniline. Chem. Phys. Lett. 1983, 95 (2), 106– 108, DOI: 10.1016/0009-2614(83)85076-352https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXhtFKmsrc%253D&md5=f1c59eb984ec398326458aa69b528778Time-dependent mass spectra and breakdown graphs. The kinetic shift in anilineLifshitz, C.; Gotchiguian, P.; Roller, R.Chemical Physics Letters (1983), 95 (2), 106-8CODEN: CHPLBC; ISSN:0009-2614.Time-resolved appearance energies and metastable peak shapes were detd. by trapped-ion mass spectrometry (TIMS) for the unimol. dissocn. of aniline cations. The long-time (milliseconds) appearance energy (AE) limit, AE(C5H6+) = 11.26 ± 0.2 eV, suggests the formation at threshold energies of the cyclopentadienyl cation with neutral HNC.
- 53Rinehart, K. L.; Buchholz, A. C.; Van Lear, G. E. Mass Spectral Fragmentation of Aniline-1-13C. J. Am. Chem. Soc. 1968, 90 (4), 1073– 1075, DOI: 10.1021/ja01006a05053https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXntleruw%253D%253D&md5=5bf834f9073f11cd14fc32b864d5d948Mass spectral fragmentation of aniline-1-carbon-13Rinehart, Kenneth L., Jr.; Buchholz, Allan C.; Van Lear, George E.Journal of the American Chemical Society (1968), 90 (4), 1073-5CODEN: JACSAT; ISSN:0002-7863.The low and high resoln. mass spectral peaks for PhNH2-1-13C were examd. The relative abundance of the isobaric peaks were measured. The results showed that most of the ions which have lost N have also lost 13C and most of those that retain N retain 13C. For the ions C5H6(-HCN) and C4H5N (-C2H2), as well as C4H3N, more than 90% of the ions arise from an unrearranged parent ion. C5H5+ and C4H4M+ are formed from C6H6N+ through the loss of HCN and C2H2, resp. The parent ion C6H7N is an odd electron ion which can lose either HCN and C2H2 directly or can rearrange to an even-electron ion while losing a H atom.
- 54Choe, J. C. Does the Gaseous Aniline Cation Isomerize to Methylpyridine Cations before Dissociation?. Bull. Korean Chem. Soc. 2013, 34 (11), 3249– 3252, DOI: 10.5012/bkcs.2013.34.11.324954https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFWqtLzF&md5=f84465a4e513c2f90026f277000c69caIsomerization of gaseous aniline cation to methylpyridine cations before dissociationChoe, Joong ChulBulletin of the Korean Chemical Society (2013), 34 (11), 3249-3252CODEN: BKCSDE; ISSN:0253-2964. (Korean Chemical Society)The potential energy surface for the isomerization of the aniline (AN) radical cation to the 2-, 3-, and 4-methylpyridine (picoline, MP) radical cations using G3 model calcns has been studied. The isomerization may occur through the 1H-azepine (7-aza-cycloheptatriene) radical cation. A quant. kinetic anal. has been performed using the Rice-Ramsperger-Kassel-Marcus theory, based on the potential energy surface. The result showed that isomerization between AN+ radical and each MP+ radical hardly occurs before their dissocns.
- 55Hedaya, E.; Kent, M. E.; McNeil, D. W.; Lossing, F. P.; McAllister, T. The Thermal Rearrangement of Phenylnitrene to Cyanocyclopentadiene. Tetrahedron Lett. 1968, 9 (30), 3415– 3420, DOI: 10.1016/S0040-4039(00)89507-6There is no corresponding record for this reference.
- 56Vuitton, V.; Yelle, R. V.; Klippenstein, S. J.; Hörst, S. M.; Lavvas, P. Simulating the Density of Organic Species in the Atmosphere of Titan with a Coupled Ion-Neutral Photochemical Model. Icarus 2019, 324, 120– 197, DOI: 10.1016/j.icarus.2018.06.01356https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktVKntrk%253D&md5=2ebec19e2c2cdc8671c887bb0769bcbcSimulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical modelVuitton, V.; Yelle, R. V.; Klippenstein, S. J.; Horst, S. M.; Lavvas, P.Icarus (2019), 324 (), 120-197CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)We present a one-dimensional coupled ion-neutral photochem. kinetics and diffusion model to study the atm. compn. of Titan in light of new theor. kinetics calcns. and scientific findings from the Cassini-Huygens mission. The model extends from the surface to the exobase. The atm. background, boundary conditions, vertical transport and aerosol opacity are all constrained by the Cassini-Huygens observations. The chem. network includes reactions between hydrocarbons, nitrogen and oxygen bearing species. It takes into account neutrals and both pos. and neg. ions with masses extending up to 116 and 74 u, resp. We incorporate high-resoln. isotopic photoabsorption and photodissocn. cross sections for N2 as well as new photodissocn. branching ratios for CH4 and C2H2. Ab initio transition state theory calcns. are performed in order to est. the rate coeffs. and products for crit. reactions. Main reactions of prodn. and loss for neutrals and ions are quant. assessed and thoroughly discussed. The vertical distributions of neutrals and ions predicted by the model generally reproduce observational data, suggesting that for the small species most chem. processes in Titan's atm. and ionosphere are adequately described and understood; some differences are highlighted. Notable remaining issues include (i) the total pos. ion d. (essentially HCNH+) in the upper ionosphere, (ii) the low mass neg. ion densities (CN-,C3N-/C4H-) in the upper atm., and (iii) the minor oxygen-bearing species (CO2, H2O) d. in the stratosphere. Pathways towards complex mols. and the impact of aerosols (UV shielding, at. and mol. hydrogen budget, nitriles heterogeneous chem. and condensation) are evaluated in the model, along with lifetimes and solar cycle variations.
- 57Dubois, D.; Carrasco, N.; Jovanovic, L.; Vettier, L.; Gautier, T.; Westlake, J. Positive Ion Chemistry in an N2-CH4 Plasma Discharge: Key Precursors to the Growth of Titan Tholins. Icarus 2020, 338, 113437, DOI: 10.1016/j.icarus.2019.11343757https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisFSrsrbE&md5=e816d28bdf36b79137c66407225e382fPositive ion chemistry in an N2-CH4 plasma discharge: Key precursors to the growth of Titan tholinsDubois, David; Carrasco, Nathalie; Jovanovic, Lora; Vettier, Ludovic; Gautier, Thomas; Westlake, JosephIcarus (2020), 338 (), 113437CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)Titan is unique in the solar system as it hosts a dense atm. mainly made of mol. nitrogen N2 and methane CH4. The Cassini Huygens Mission revealed the presence of an intense atm. photochem. initiated by the photo dissocn. and ionization of N2 and CH4. In the upper atm., Cassini detected signatures compatible with the presence of heavily charged mols. which are precursors for the solid core of the aerosols. These observations have indicated that ion chem. has an important role for org. growth. However, the processes coupling ion chem. and aerosol formation and growth are still mostly unknown. In this study, we investigated the cation chem. responsible for an efficient org. growth that we observe in Titan's upper atm., simulated using the PAMPRE plasma reactor. Pos. ion precursors were measured by in situ ion mass spectrometry in a cold plasma and compared with INMS observations taken during the T40 flyby. A series of pos. ion measurements were performed in three CH4 mixing ratios (1%, 5% and 10%) showing a variability in ion population. Low methane concns. result in an abundance of amine cations such as NH+4 whereas aliph. compds. dominate at higher methane concns. In conditions of favored tholin prodn., the presence of C2 compds. such as HCNH+ and C2H+5 is found to be consistent with copolymeric growth structures seen in tholin material. The obsd. abundance of these two ions particularly in conditions with lower CH4 amts. is consistent with modeling work simulating aerosol growth in Titan's ionosphere, which includes mass exchange primarily between HCNH+ and C2H+5 and neg. charged particles. These results also confirm the prevalent role of C2 cations as precursors to mol. growth and subsequent mass transfer to the charged aerosol particles as the CH4 abundance decreases towards lower altitudes.
- 58Lavvas, P.; Galand, M.; Yelle, R. V.; Heays, A. N.; Lewis, B. R.; Lewis, G. R.; Coates, A. J. Energy Deposition and Primary Chemical Products in Titan’s Upper Atmosphere. Icarus 2011, 213 (1), 233– 251, DOI: 10.1016/j.icarus.2011.03.00158https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXltlGgu7Y%253D&md5=a50aa0409b282d6ec14b86c86aa01d57Energy deposition and primary chemical products in Titan's upper atmosphereLavvas, P.; Galand, M.; Yelle, R. V.; Heays, A. N.; Lewis, B. R.; Lewis, G. R.; Coates, A. J.Icarus (2011), 213 (1), 233-251CODEN: ICRSA5; ISSN:0019-1035. (Elsevier B.V.)Cassini results indicate that solar photons dominate energy deposition in Titan's upper atm. These dissoc. and ionize nitrogen and methane and drive the subsequent complex org. chem. The improved constraints on the atm. compn. from Cassini measurements demand greater precision in the photochem. modeling. Therefore, in order to quantify the role of solar radiation in the primary chem. prodn., we have performed detailed calcns. for the energy deposition of photons and photoelectrons in the atm. of Titan and we validate our results with the Cassini measurements for the electron fluxes and the EUV/FUV emissions. We use high-resoln. cross sections for the neutral photodissocn. of N2, which we present here, and show that they provide a different picture of energy deposition compared to results based on low-resoln. cross sections. Furthermore, we introduce a simple model for the energy degrdn. of photoelectrons based on the local deposition approxn. and show that our results are in agreement with detailed calcns. including transport, in the altitude region below 1200 km, where the effects of transport are negligible. Our calcd., daytime, electron fluxes are in good agreement with the measured fluxes by the Cassini Plasma Spectrometer (CAPS), and the same holds for the measured FUV emissions by the UV Imaging Spectrometer (UVIS). Finally, we present the vertical prodn. profiles of radicals and ions originating from the interaction of photons and electrons with the main components of Titan's atm., along with the column integrated prodn. rates at different solar zenith angles. These can be used as basis for any further photochem. calcns.
- 59Galand, M.; Yelle, R.; Cui, J.; Wahlund, J. E.; Vuitton, V.; Wellbrock, A.; Coates, A. Ionization Sources in Titan’s Deep Ionosphere. J. Geophys. Res. Space Phys. 2010, 115 (7), 7312, DOI: 10.1029/2009JA01510059https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlWrsbbK&md5=404eef0f463585494baabfdeac44732dIonization sources in Titan's deep ionosphereGaland, Marina; Yelle, Roger; Cui, Jun; Wahlund, Jan-Erik; Vuitton, Veronique; Wellbrock, Anne; Coates, AndrewJournal of Geophysical Research, [Space Physics] (2010), 115 (A7), A07312/1-A07312/14CODEN: JJGPD4 ISSN:. (American Geophysical Union)We analyze a multi-instrumental data set from four Titan encounters by the Cassini spacecraft to investigate in detail the formation of the ionosphere. The data set includes observations of thermospheric and ionospheric species and suprathermal electrons. A model describing the solar and electron energy deposition is used as an organizing element of the Cassini data set. We first compare the calcd. secondary electron prodn. rates with the rates inferred from suprathermal electron intensity measurements. We then calc. an effective electron dissociative recombination coeff., applying three different approaches to the Cassini data set. Our findings are threefold: (1) The effective recombination coeff. derived under sunlit conditions in the deep ionosphere (<1200 km) is found to be independent of solar zenith angle and flyby. Its value ranges from 6.9 × 10-7 cm3 s-1 at 1200 km to 5.9 × 10-6 cm3 s-1 at 970 km at 500 K. (2) The presence of an addnl., minor source of ionization is revealed when the solar contribution is weak enough. The contribution by this non-solar source-energetic electrons most probably of magnetospheric origin-becomes apparent for secondary electron prodn. rates, due to solar illumination alone, close to or smaller than about 3 × 10-1 cm-3 s-1. Such a threshold is reached near the solar terminator below the main solar-driven electron prodn. peak (<1050 km). (3) Our ability to model the electron d. in the deep ionosphere is very limited. Our findings highlight the need for more lab. measurements of electron dissociative recombination coeffs. for heavy ion species at high electron temps. (esp. near 500 K).
- 60Puzzarini, C.; Barone, V. A Never-Ending Story in the Sky: The Secrets of Chemical Evolution. Phys. Life Rev. 2020, 32, 59– 94, DOI: 10.1016/j.plrev.2019.07.00160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3MzovVSjsg%253D%253D&md5=2bea3a3f04dd5d61d3088c1bb572c57bA never-ending story in the sky: The secrets of chemical evolutionPuzzarini Cristina; Barone VincenzoPhysics of life reviews (2020), 32 (), 59-94 ISSN:.Cosmic evolution is the tale of progressive transition from simplicity to complexity. The newborn universe started with the simplest atoms formed after the Big Bang and proceeded toward the formation of the so-called 'astronomical complex organic molecules' (aCOMs), most of them showing a clear prebiotic character. Understanding the chemical evolution of the universe is one of the main aims of Astrochemistry, with the starting point being the knowledge whether a molecule is present in the astronomical environment under consideration and, if so, its abundance. However, the interpretation of astronomical detections and the identification of molecules are not at all straightforward. Indeed, the extraterrestrial chemical inventory has been obtained by means of astronomical observations based on spectroscopic signatures determined in laboratory (either experimental or computational) studies. Even though the presence of aCOMs has been known for decades, the processes that lead to their synthesis are still hotly debated or even unknown. It is often assumed that aCOMs are mostly synthesized on grain surfaces during the so-called warm-up phase, when various radicals trapped in the grain mantles acquire mobility and recombine into large molecules. However, recent detections of aCOMs in cold environments have challenged this exclusive role of grain-surface chemistry. Clearly, gas-phase chemistry is at work in cold environments. Moving to Titan's atmosphere, prior to the Cassini-Huygens arrival in the Saturn system, it was generally believed that Earth and interstellar space are the two places where organic molecules are/were synthesized extensively. However, the experimental measurements by the instruments on board the Cassini orbiter spacecraft and the Huygens probe lander have changed this view. To disclose the "secrets" of chemical evolution across space, the first step is the understanding of how small prebiotic species are formed and how the chemical complexity can further increase. This review indeed addresses the chemical evolution in space, focusing - in particular - on the role played by molecular spectroscopy and quantum-chemical computations. To summarize, in this review we will first of all present how the signatures of molecules can be found in space. Then, we will address, from a computational point of view, the derivation of the molecular spectroscopic features, the investigation of gas-phase formation routes of prebiotic species in the ISM, and the evolution of chemical complexity, from small molecules to haze, in Titan's atmosphere. Finally, an integrated strategy, also involving high-performance computers and virtual reality, will be discussed.
- 61Hendrix, J.; Bera, P. P.; Lee, T. J.; Head-Gordon, M. Cation, Anion, and Radical Isomers of C4H4N: Computational Characterization and Implications for Astrophysical and Planetary Environments. J. Phys. Chem. A 2020, 124 (10), 2001– 2013, DOI: 10.1021/acs.jpca.9b1130561https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjsV2mtbw%253D&md5=268549e5488895704e5c72dbc1587b1cCation, Anion, and Radical Isomers of C4H4N: Computational Characterization and Implications for Astrophysical and Planetary EnvironmentsHendrix, Josie; Bera, Partha P.; Lee, Timothy J.; Head-Gordon, MartinJournal of Physical Chemistry A (2020), 124 (10), 2001-2013CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)Nitrogen-contg. ions and mols. in the gas phase have been detected in non-Earth environments such as dark mol. clouds and more recently in the atm. of Saturn's moon Titan. These mols. may serve as precursors to larger heterocyclic structures that provide the foundation of complex biol. mols. On Titan, mols. of m/z 66 have been detected by the Cassini mission, and species of the empirical formula C4H4N may contribute to this signature. We have characterized seven isomers of C4H4N in anionic, neutral radical, and cationic states using d. functional theory. Structures were optimized using the range-sepd. hybrid ωB97X-V with the cc-pVTZ and aug-cc-pVTZ basis sets. Anionic and radical C4H4N favor cyclic structures with arom. and quasi-arom. electron arrangements, resp. Interestingly, ionization from the radical surface to the cation induces significant changes in structural stability, and the global min. for pos. charged isomers is CH2CCHCNH+, a pseudo-linear species reminiscent of cyanoallene. Select formation pathways to these structures from Titan's existing or postulated gas-phase species, reactions that are also relevant for other astrophys. environments, are discussed. By characterizing C4H4N isomers, we have identified energetically stable anionic, radical, and cationic structures that may be present in Titan's atm. and dark mol. clouds.
- 62Dobrijevic, M.; Loison, J. C.; Hickson, K. M.; Gronoff, G. 1D-Coupled Photochemical Model of Neutrals, Cations and Anions in the Atmosphere of Titan. Icarus 2016, 268, 313– 339, DOI: 10.1016/j.icarus.2015.12.04562https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtlaju7k%253D&md5=adb4d23fb21e2b8fa006395f643f6e4e1D-coupled photochemical model of neutrals, cations and anions in the atmosphere of TitanDobrijevic, M.; Loison, J. C.; Hickson, K. M.; Gronoff, G.Icarus (2016), 268 (), 313-339CODEN: ICRSA5; ISSN:0019-1035. (Elsevier Inc.)Many models with different characteristics have been published so far to study the chem. processes at work in Titan's atm. Some models focus on neutral species in the stratosphere or ionic species in the ionosphere, but few of them couple all the species throughout the whole atm. Very few of these emphasize the importance of uncertainties in the chem. scheme and study their propagation in the model.We have developed a new 1D-photochem. model of Titan's atm. coupling neutral species with pos. and neg. ions from the lower atm. up to the ionosphere and have compared our results with observations to have a comprehensive view of the chem. processes driving the compn. of the stratosphere and ionosphere of Titan. We have updated the neutral, pos. ion and neg. ion chem. and have improved the description of N2 photodissocn. by introducing high resoln. N2 absorption cross sections. We performed for the first time an uncertainty propagation study in a fully coupled ion-neutral model.We det. how uncertainties on rate consts. on both neutral and ionic reactions influence the model results and pinpoint the key reactions responsible for this behavior. We find very good agreement between our model results and observations in both the stratosphere and in the ionosphere for most neutral compds. COur results are also in good agreement with an av. INMS mass spectrum and specific flybys in the dayside, suggesting that our chem. model (for both neutral and ions) provides a good approxn. of Titan's atm. chem. as a whole. Our uncertainty propagation study highlights the difficulty to interpret the INMS mass spectra for masses 14, 31, 41 and we identified the key reactions responsible for these ambiguities.Despite an overall improvement in the chem. model, disagreement for some specific compds. (HC3N, C2H5CN, C2H4) highlights the role that certain phys. processes could play (meridional dynamics or sticking on aerosols). We find that some crit. key reactions are important for many compds. including both neutrals and ions and should be studied in priority to lower the remaining model uncertainties. Extensive studies for some specific processes (including photolyses) are required.
- 63De Haas, A. J.; Oomens, J.; Bouwman, J. Facile Pentagon Formation in the Dissociation of Polyaromatics. Phys. Chem. Chem. Phys. 2017, 19 (4), 2974– 2980, DOI: 10.1039/C6CP08349H63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFehtbrM&md5=1c6afb975e816910eae3431d2f381ff2Facile pentagon formation in the dissociation of polyaromaticsde Haas, Arjen J.; Oomens, Jos; Bouwman, JordyPhysical Chemistry Chemical Physics (2017), 19 (4), 2974-2980CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Energetic processing of gaseous polycyclic arom. hydrocarbons (PAHs) plays a pivotal role in the chemistries of inter- and circumstellar environments, certain planetary atmospheres, and also in the chem. of combustion and soot formation. Although the precursor PAH species have been extensively characterized, the products from these gaseous breakdown reactions have received far less attention. It has been particularly challenging to accurately det. their mol. structure in gas-phase expts., where comparisons against theor. modeling are best made. Here we report on a combined exptl. and theor. study of the dissociative ionization of two nitrogen contg. polycyclic arom. hydrocarbons of C13H9N compn., acridine and phenanthridine. The structures of HCN-loss fragments are resolved by IR multiple-photon dissocn. (IRMPD) spectroscopy of the mass-isolated products in an ion trap mass spectrometer. Quantum-chem. computations as well as ref. IRMPD spectra are employed to unambiguously identify the mol. structures. Furthermore, computations at the d. functional level of theory provide insight into chem. pathways leading to the obsd. products. Acenaphthylene·+ and benzopentalene·+ - two arom. species contg. pentagons - are identified as the main products, suggesting that such species are easily formed and may be abundant in regions where thermal or photoprocessing of polyaroms. occurs.
- 64Marciniak, A.; Joblin, C.; Mulas, G.; Mundlapati, V. R.; Bonnamy, A. Photodissociation of Aliphatic PAH Derivatives under Relevant Astrophysical Conditions. Astron. Astrophys. 2021, 652, A42, DOI: 10.1051/0004-6361/20214073764https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitFyhsbjN&md5=ff4423faab446b974c869602fc692c02Photodissociation of aliphatic PAH derivatives under relevant astrophysical conditionsMarciniak, A.; Joblin, C.; Mulas, G.; Mundlapati, V. Rao; Bonnamy, A.Astronomy & Astrophysics (2021), 652 (), A42CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)The interaction of polycyclic arom. hydrocarbons (PAHs) with vacuum UV (VUV) photons triggers the emission of the well-known arom. IR bands (AIBs), but other mechanisms, such as fragmentation, can be involved in this interaction. Fragmentation leads to selection effects that favor specific sizes and structures. Our aim is to investigate the impact of aliph. bonds on the VUV photostability of PAH cations in a cryogenic and collisionless environment with conditions applicable for photodissocn. regions (PDRs). The studied species are derived from pyrene (C16H10) and coronene (C24H12) and contain aliph. bonds either in the form of Me or Et sidegroups or of superhydrogenation. Their cations are produced by laser desorption ionization and isolated in the cryogenic ion cell of the PIRENEA setup, where they are submitted to VUV photons of 10.5 eV energy over long timescales (∼1000 s). The parent and fragment ions are mass-analyzed and their relative intensities are recorded as a function of the irradn. time. The fragmentation cascades are analyzed with a simple kinetics model from which we identify fragmentation pathways and derive fragmentation rates and branching ratios for both the parents and their main fragments. Aliph. PAH derivs. are found to have a higher fragmentation rate and a higher carbon to hydrogen loss compared to regular PAHs. On the other hand, the fragmentation of PAHs with alkylated sidegroups forms species with peripheral pentagonal cycles, which can be as stable as, or even more stable than, the bare PAH cations. This stability is quantified for the main ions involved in the fragmentation cascades by the comparison of the fragmentation rates with the photoabsorption rates derived from theor. photoabsorption cross sections. The most stable species for which there is an effective competition of fragmentation with isomerization and radiative cooling are identified, providing clues on the structures favored in PDRs. Conclusions. This work supports a scenario in which the evapn. of nanograins with a mixed aliph. and arom. compn. followed by VUV photoprocessing results in both the prodn. of the carriers of the 3.4 μm AIB by Me sidegroups and in an abundant source of small hydrocarbons at the border of PDRs. An addnl. side effect is the efficient formation of stable PAHs that contain some peripheral pentagonal rings. Our expts. also support the role of isomerization processes in PAH photofragmentation, including the H-migration process, which could lead to an addnl. contribution to the 3.4 μm AIB.
- 65Rodriguez Castillo, S.; Simon, A.; Joblin, C. Investigating the Importance of Edge-Structure in the Loss of H/H2 of PAH Cations: The Case of Dibenzopyrene Isomers. Int. J. Mass Spectrom. 2018, 429, 189– 197, DOI: 10.1016/j.ijms.2017.09.01365https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslehtrfF&md5=a1061550b03f54d90d93212f5e8d92e8Investigating the importance of edge-structure in the loss of H/H2 of PAH cations: The case of dibenzopyrene isomersRodriguez Castillo, Sarah; Simon, Aude; Joblin, ChristineInternational Journal of Mass Spectrometry (2018), 429 (), 189-197CODEN: IMSPF8; ISSN:1387-3806. (Elsevier B.V.)We present a detailed study of the main dehydrogenation processes of two dibenzopyrene cation (C24H+14) isomers, namely dibenzo(a,e)pyrene (AE+) and dibenzo(a,l)pyrene (AL+). First, action spectroscopy under VUV photons was performed using synchrotron radiation in the 8-20 eV range. We obsd. lower dissocn. thresholds for the non-planar mol. (AL+) than for the planar one (AE+) for the main dissocn. pathways: H and 2H/H2 loss. In order to rationalize the exptl. results, dissocn. paths were investigated by means of d. functional theory calcns. In the case of H loss, which is the dominant channel at the lowest energies, the obsd. difference between the two isomers can be explained by the presence in AL+ of two C-H bonds with considerably lower adiabatic dissocn. energies. In both isomers the 2H/H2 loss channels are obsd. only at about 1 eV higher than H loss. We suggest that this is due to the propensity of bay H atoms to easily form H2. In addn., in the case of AL+, we cannot exclude a competition between 2H and H2 channels. In particular, the formation of a stable dissocn. product with a five-membered ring could account for the low energy sequential loss of 2 hydrogens. This work shows the potential role of non-compact PAHs contg. bay regions in the prodn. of H2 in space.
- 66Cernicharo, J.; Agúndez, M.; Kaiser, R. I.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; De Vicente, P. Discovery of Two Isomers of Ethynyl Cyclopentadiene in TMC-1: Abundances of CCH and CN Derivatives of Hydrocarbon Cycles. Astron. Astrophys. 2021, 655, L1, DOI: 10.1051/0004-6361/20214222666https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XitVWltr8%253D&md5=b18da27021abbe28603d962096606617Discovery of two isomers of ethynyl cyclopentadiene in TMC-1 and abundances of CCH and CN derivatives of hydrocarbon cyclesCernicharo, J.; Agundez, M.; Kaiser, R. I.; Cabezas, C.; Tercero, B.; Marcelino, N.; Pardo, J. R.; de Vicente, P.Astronomy & Astrophysics (2021), 655 (), L1CODEN: AAEJAF; ISSN:1432-0746. (EDP Sciences)We report the detection of two isomers of ethynyl cyclopentadiene (c-C5H5CCH), namely 1- and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4 ± 0.2) x 1012 cm-2 and (2.0 ± 0.4) x 1012 cm-2, resp., for these two cyclopentadiene derivs., which imply that they are about ten times less abundant than cyclopentadiene. We also report the tentative detection of ethynyl benzene (C6H5CCH), for which we est. a column d. of (2.5 ± 0.4) x 1012 cm-2. We derived abundances for the corresponding cyano derivs. of cyclopentadiene and benzene and found values significantly lower than previously reported. The rotational temp. of the ethynyl and cyano derivs. of these cycles is about 9 K, i.e., very close to the gas kinetic temp. of the cloud. The abundance ratio of the 1- and 2-isomers of ethynyl cyclopentadiene is 1.4 ± 0.5, while for the two isomers of cyano cyclopentadiene it is 2.4 ± 0.6. The relative abundances of CCH over CN derivs. is 7.7 ± 2.2 for cyclopentadiene, which probably reflects the abundance ratio of the radicals CCH and CN; this ratio is only 2.1 ± 0.5 for benzene, which suggests that addnl. reactions besides cyano radicals with benzene are involved in the formation of benzonitrile. The formation of these cycles is reasonably well accounted for through a chem. scheme based on neutral-neutral reactions. It is predicted that benzene should be as abundant as cyclopentadiene in TMC-1.
- 67Cernicharo, J.; Marcelino, N.; Agúndez, M.; Endo, Y.; Cabezas, C.; Bermúdez, C.; Tercero, B.; De Vicente, P. Discovery of HC3O+ in Space: The Chemistry of O-Bearing Species in TMC-1. Astron. Astrophys. 2020, 642, L17, DOI: 10.1051/0004-6361/202039351There is no corresponding record for this reference.
- 68Hunter, E. P. L.; Lias, S. G. Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update. J. Phys. Chem. Ref. Data 1998, 27 (3), 413– 656, DOI: 10.1063/1.55601868https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXjvVKgtLs%253D&md5=4dc92e07c2bc4f423b644c8ca54aca3aEvaluated Gas Phase Basicities and Proton Affinities of Molecules: An UpdateHunter, Edward P. L.; Lias, Sharon G.Journal of Physical and Chemical Reference Data (1998), 27 (3), 413-656CODEN: JPCRBU; ISSN:0047-2689. (American Chemical Society)A review with more than 70 refs. The available data on gas-phase basicities and proton affinities of approx. 1700 mol., radical, and at. neutral species are evaluated and compiled. Tables of the data are sorted (1) according to empirical formula and (2) according to evaluated gas basicity. This publication constitutes an update of a similar evaluation published in 1984.
- 69Botschwina, P. A Theoretical Investigation of the Astrophysically Important Molecules C3O and HC3O+. J. Chem. Phys. 1989, 90 (8), 4301– 4312, DOI: 10.1063/1.45578769https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXks1Cgt7w%253D&md5=1d265443795c5fea6a32756ec7b60dc6A theoretical investigation of the astrophysically important molecules tricarbon monoxide and protonated tricarbon monoxide (C3O and HC3O+)Botschwina, PeterJournal of Chemical Physics (1989), 90 (8), 4301-13CODEN: JCPSA6; ISSN:0021-9606.Large-scale CEPA calcns. were carried out for the astrophys. important mols. C3O and HC3O+. C3O has a linear equil. geometry with short terminal CC and CO bond lengths of 1.273 and 1.149 Å and a central CC equil. bond length of 1.300 Å. Upon protonation the terminal CC and CO bond lengths are shortened by 0.061 and 0.026 Å, resp., while the central CC bond length experiences an elongation by 0.052 Å. C3O has a noticeably large equil. dipole moment of 2.535 D with the pos. end at the oxygen site. The IR intensity of the ν1 band at 2229 cm-1 is extremely large (72 756 cm2 mol-1). Although the intensity of the corresponding ν2 band of HC3O+ at 2318 cm-1 is only about one half as large this band appears to be most promising for future IR diode laser investigation. The proton affinity of C3O at 298 K is 885 ± 5 kJ mol-1.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpca.2c01429.
Mass spectrum of m/z 92 Ne tagging; saturation depletion scans (PDF)
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