Ultraviolet resonance Raman scattering of azulene: A test of transform theory

Abstract

Raman excitation profiles (REPs) from a highly excited state in azulene are presented for several vibrational modes. These include four fundamentals, a combination, and an overtone. Experimental REPs are compared to transform theory predictions which are based on the observable absorption spectrum (ABS) of the resonant electronic state. Though both the REPs and the ABS are multimode in nature, the transform provides a single mode link between the two and allows for extraction of excited state parameters on a mode by mode basis. For several modes, excited state frequencies and Franck–Condon coupling constants are estimated. Observed discrepancies between experiment and transform for other modes raise questions as to the applicability of the ‘‘standard assumptions’’ on which the transform is based to all of the vibrational modes in this electronic state. The strongly enhanced Raman scattering also allows depolarization ratios to be determined for all the azulene symmetric ring vibrations and directly confirms previous symmetry assignments.