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

The first resonance Raman spectra of benzene and deuterobenzene are reported. Resonance excitation with the second excited singlet transition ( ¹B_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 v₁, 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 v_g e_2g mode is found to be the most vibronically active mode in the ¹B_1u transition, in agreement with all calculations. However, in contrast to these calculations, the Raman analysis finds that v₉, not v₆, is the next most vibronically active e_2g mode in this transition. These results parallel the observed pattern of vibronic intensities in the ³B_1u→¹A_1g phosphorescence spectra.