Resonance Raman scattering of benzene and benzene-d6 with 212.8 nm excitation

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Abstract
The first resonance Raman spectra of benzene and deuterobenzene are reported. Resonance excitation with the second excited singlet transition (1 B 1u ) is obtained with 212.8 nm radiation. These resonance Raman spectra are dominated by the overtones and combinations of the vibronically active e 2g modes in this dipole forbidden transition, as well as the fundamental, overtone, and combination of ν1, the a 1g ring breathing mode. All of the observed features, including relative intensities and depolarization ratios, are fully rationalized within the context of the vibronic theory once the 3N‐6 multidimensionality of the vibrational sublevels is exposed. The ν8 e 2g mode is found to be the most vibronically active mode in the 1 B 1u transition, in agreement with all calculations. However, in contrast to these calculations, the Raman analysis finds that ν9, not ν6, is the next most vibronically active e 2g mode in this transition. These results parallel the observed pattern of vibronic intensities in the 3 B 1u →1 A 1g phosphorescence spectra.