The benzene ground state potential surface. I. Fundamental frequencies for the planar vibrations

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Abstract
The accuracy of vapor phase vibrational data has been improved for all 12 deuterium-labeled benzenes and for 13C12C5H6 and 13C6H6. Many vapor phase fundamental frequencies are observed for the first time. Precise isotopic frequency/splitting patterns for ν1, ν18, and ν19 have been obtained. Isotope induced harmonic mode mixing matrices are given for all 14 labeled benzenes and used to provide detailed description of the fundamental bands observed in the spectra. These descriptions provide numerous reassignments for the fundamental bands, particularily in low symmetry deuterium benzenes. The matrices show that some skeletal modes, such as ν1, gain CH stretching character as a result of deuterium labeling, providing a rationalization for the increased anharmonicity observed in recent jet experiments for C6D6. In addition, a reassessment of Fermi resonance gives 3072.3 cm−1 for the unperturbed frequency (correction +24 cm−1) for the e1u mode ν20 in C6H6 refining the CH local mode anharmonic constant, 2xii, to 117.5 cm−1.