Dynamics of intramolecular vibrational-energy redistribution (IVR). IV. Excess energy dependence, t-stilbene

The results of picosecond time-resolved measurements of intramolecular vibrational-energy redistribution (IVR) in jet-cooled t-stilbene are presented. The results show that the changes in the nature of IVR that were found to occur with increasing energy in anthracene also occur in t-stilbene. In particular, at intermediate energies a number of different excitations give rise to phase-shifted quantum beats in fluorescence decays, indicating restricted IVR in the molecule. At higher energies decay behavior characteristic of dissipative IVR is observed. These results are compared with those of anthracene and are discussed in terms of molecular symmetry and vibrational density of states. The results suggest the generality of the conclusions about large molecule IVR that have been stated in the other papers of this series