Raman scattering of benzene in the ultraviolet,

The excitation frequency dependence of intensities of the Raman active fundamentals of benzene have been measured in the uv spectral region approaching the low lying forbidden electronic states (the 1B2u and 1B1u). In accordance with theory, these forbidden states do not cntribute to the scattering cross section of any fundamental in this preresonance region. Furthermore, all but one scattering mode (the e1g vibration) are found to derive their intensity from state in the deep vacuum uv (120 nm or above) and not the familiar strongly allowed ππ* 1E1u state at 185 nm. By contrast Raman scattering of the e1g mode (848 cm−1) appears to be derived from vibronic coupling between this 1E1u state and a weakly allowed nearby 1A2u state.