Web Release Date: January 27,
Cu3C4-: A New Sandwich Molecule with Two Revolving C22- Units
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300
Department of Physics, Washington State University, 2710 University Drive, Richland, Washington 99352, and W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, MS K8-88, P.O. Box 999, Richland, Washington 99352
Received: June 16, 2004
In Final Form: October 4, 2004
Abstract:
A combined photoelectron spectroscopy (PES) and ab initio study was carried out on a novel copper carbide
cluster in the gas phase: Cu3C4-. It was generated in a laser vaporization cluster source and appeared to
exhibit enhanced stability among the Cu3Cn- series. Its PES spectra were obtained at several photon energies,
showing numerous well-resolved bands. Extensive ab initio calculations were performed on Cu3C4-, and two
isomers were identified: a C2 structure (1A) with a Cu33+ triangular group sandwiched by two C22- units and
a linear CuCCCuCCCu structure (D
h, 1
g+). A comparison of ab initio PES spectra with experimental data
showed that the sandwich Cu3C4- cluster was solely responsible for the observed spectra and the linear isomer
was not present, suggesting that the C2 structure is the global minimum in accordance with CCSD(T)/6-311+G* predictions. Interestingly, a relatively low barrier (0.4-0.6 kcal/mol) was found for the internal
rotation of the C22- units in the sandwich Cu3C4-. To test different levels of theory in describing the CumCn-
systems and lay foundations for the validity of the theoretical methods, extensive calculations at a variety of
levels were also carried out on a simpler copper carbide species CuC2-, where two isomers were found to be
close in energy: a linear one (Cv, 1+) and a triangular one (C2v, 1A1). The calculated electronic transitions
for CuC2- were also compared with the PES data, in which both isomers were present.
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