ORIGIN OF DEPOLARIZATION DISPERSION OF TOTALLY SYMMETRICAL 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 depo larization ratio of totally symmetric fundamentals, in the excitation range of resonance Raman scattering of cis-polyacetylene. The first mo del works in the diabatic approach of the vibronic coupling theory, an d considers a solvent-induced symmetry lowering as a probable mechanis m for inducing scattering of totally symmetric motions into a forbidde n electronic transition. The second one is based on the theory develop ed by Korenowski, Ziegler, and Albrecht and assumes that even dipole-f orbidden electronic states are possible sources for the Raman-intensit y enhancements and for the dispersion of depolarization ratios when a vibrational mixing mode produces vibronic coupling between forbidden a nd allowed electronic states. Both models seem to be suitable, even if with some differences, for fitting our experimental results for two t otally symmetric motions of a soluble form of cis-polyacetylene.