RESONANCE DE-ENHANCEMENT IN THE 2(1)A(G) STATE OF TRANS-AZOBENZENE

We analyze the origin of de-enhancement for a number of vibrational mo des in the 2(1)A(g) excited state of trans-azobenzene. We have used th e time-dependent wave packet analysis of the RR intensities by includi ng the multimode damping effects in the calculation. This avoids the u se of unrealistically large values for the damping parameter. It is co ncluded that the de-enhancement is caused by the interference between the two uncoupled electronic states, and that the intensities observed under the so-called symmetry forbidden 2(1)A(g) <-- 1(1)A(g) transiti on are purely due to resonance excitation. It is also observed that th e use of the time-dependent approach to study the de-enhancement effec ts caused by multiple electronic states on the RR intensities is not n ecessarily useful if one is interested in the structural dynamics.