Origin of depolarization dispersion of totally symmetric fundamental transitions in the resonance Raman effect of soluble cis-polyacetylene

Two models are presented which we have used to reproduce experimental data, such as Raman excitation profiles and the dispersion of the depolarization ratio of totally symmetric fundamentals, in the excitation range of resonance Raman scattering of cis-polyacetylene. The first model works in the diabatic approach of the vibronic coupling theory, and considers a solvent-induced symmetry lowering as a probable mechanism for inducing scattering of totally symmetric motions into a forbidden electronic transition. The second one is based on the theory developed by Korenowski, Ziegler, and Albrecht and assumes that even dipole-forbidden electronic states are possible sources for the Raman-intensity enhancements and for the dispersion of depolarization ratios when a vibrational mixing mode produces vibronic coupling between forbidden and allowed electronic states. Both models seem to be suitable, even if with some differences, for fitting our experimental results for two totally symmetric motions of a soluble form of cis-polyacetylene.