A PICOSECOND TIME-RESOLVED RESONANCE RAMAN-STUDY OF S-1 CIS-STILBENE

The time-resolved resonance Raman (TR3) spectrum of S-1 cis-stilbene i n n-hexane is presented. Raman bands are observed at 243, 475, 742, 97 7, 1200 and 1440 cm(-1). Their positions and relative intensities sugg est that these belong to a high-order overtone progression (up to the fifth order) originating from the 243 cm(-1) fundamental. This observa tion implies a large difference between S-1 and the resonant S-n state s in the equilibrium nuclear coordinate corresponding to the 243 cm(-1 ) mode, with displacement Delta similar to 12. Ground and excited stat e equilibrium geometries and frequencies are determined using ab initi o molecular orbital calculations. (C) 1997 Elsevier Science B.V.