Structure and Spectroscopic Insights for CH3PCO Isomers: A High-Level Quantum Chemical Study

The exploration of phosphorus-bearing species stands as a prolific field in current astrochemical research, particularly within the context of prebiotic chemistry. Herein, we have employed high-level quantum chemistry methodologies to predict the structure and spectroscopic properties of isomers composed of a methyl group and three P, C, and O atoms. We have computed relative and dissociation energies, as well as rotational, rovibrational, and torsional parameters using the B2PLYPD3 functional and the explicitly correlated coupled cluster CCSD(T)-F12b method. Based upon our study, all the isomers exhibit a bent heavy atom skeleton with CH3PCO being the most stable structure, regardless of the level theory employed. Following in energy, we found four high-energy isomers, namely, CH3OCP, CH3CPO, CH3COP, and CH3OPC. The computed adiabatic dissociation energies support the stability of all [CH3, P, C, O] isomers against fragmentation into CH3 and [P, C, O]. Torsional barrier heights associated with the methyl internal rotation for each structure have been computed to evaluate the occurrence of possible A–E splittings in the rotational spectra. For the most stable isomer, CH3PCO, we found a V3 barrier of 82 cm–1, which is slightly larger than that obtained experimentally for the N-counterpart, CH3NCO, yet still very low. Therefore, the analysis of its rotational spectrum can be anticipated as a challenging task owing to the effect of the CH3 internal rotation. The complete set of spectroscopic constants and transition frequencies reported here for the most stable isomer, CH3PCO, is intended to facilitate eventual laboratory searches.


Figure S1 :
Figure S1: Contour maps of the Laplacian distribution of the electron density for the CH3PCO isomer.

Figure S2 :
Figure S2: Contour maps of the Laplacian distribution of the electron density for the CH3OCP isomer.

Figure S3 :
Figure S3: Contour maps of the Laplacian distribution of the electron density for the CH3CPO isomer.

Figure S4 :
Figure S4: Contour maps of the Laplacian distribution of the electron density for the CH3COP isomer.

Figure S5 :
Figure S5: Contour maps of the Laplacian distribution of the electron density for the CH3OPC isomer.

Figure S3 :
Figure S3:Contour maps of the Laplacian distribution of the electron density for the CH3CPO isomer.Red dashed lines indicate regions of electronic charge concentration (  ()< 0), and blue continuous lines denote regions of electronic charge depletion (  ()> 0).

Figure S4 :S10Figure S5 :
Figure S4: Contour maps of the Laplacian distribution of the electron density for the CH3COP isomer.Red dashed lines indicate regions of electronic charge concentration (  ()< 0), and blue continuous lines denote regions of electronic charge depletion (  ()> 0).

Table S1 :
Local Topological Properties of the Electronic Charge Density Distribution for the CH3PCO isomer

Table S2 :
Local Topological Properties of the Electronic Charge Density Distribution for the CH3OCP isomer

Table S3 :
Local Topological Properties of the Electronic Charge Density Distribution for the CH3CPO isomer

Table S4 :
Local Topological Properties of the Electronic Charge Density Distribution for the CH3COP isomer

Table S5 :
Local Topological Properties of the Electronic Charge Density Distribution for the CH3OPC isomer

Table S1 :
Local Topological Properties (in au.) of the Electronic Charge Density Distribution Calculated at the B2PLYPD3 level, at the Position of the Bond Critical Points for the CH3PCO isomer.a 2 (): Laplacian of electronic charge density; |()|/(): Relationship between the local kinetic energy density () and the local potential energy density (); (): Total energy density.

Table S2 :
Local Topological Properties (in au.) of the Electronic Charge Density Distribution Calculated at the B2PLYPD3 level, at the Position of the Bond Critical Points for the CH3OCP isomer.a

Table S3 :
Local Topological Properties (in au.) of the Electronic Charge Density Distribution Calculated at the B2PLYPD3 level, at the Position of the Bond Critical Points for the CH3CPO isomer.a Notes.(): Electronic charge density; ∇ 2 (): Laplacian of electronic charge density; |()|/(): Relationship between the local kinetic energy density () and the local potential energy density (); (): Total energy density.

Table S4 :
Local Topological Properties (in au.) of the Electronic Charge Density Distribution Calculated at the B2PLYPD3 level, at the Position of the Bond Critical Points for the CH3COP isomer.a

Table S5 :
Local Topological Properties (in au.) of the Electronic Charge Density Distribution Calculated at the B2PLYPD3 level, at the Position of the Bond Critical Points for the CH3OPC isomer.a Notes.(): Electronic charge density; ∇ 2 (): Laplacian of electronic charge density; |()|/(): Relationship between the local kinetic energy density () and the local potential energy density (); (): Total energy density.S6