THE DEVELOPMENT OF SEMICLASSICAL DYNAMICAL METHODS AND THEIR APPLICATION TO VIBRATIONAL-RELAXATION IN CONDENSED-PHASE SYSTEMS

A semiclassical surface-hopping propagator for problems involving nona diabatic transitions is discussed. The propagator is employed in expre ssions for the probability of transitions between quantum states of mo lecules in condensed phases. This approach is implemented for the eval uation of the rate of vibrational transitions in liquids, dense gases, and clusters. Results for the rates of relaxation of excited vibratio nal states of a molecule in a simple solvent are discussed. The use of computationally simplifying short-time approximations for the solvent dynamics are considered. These approximations are tested using calcul ations on simple model systems. It is found that these simplifying app roximations work well as long as the energy difference between the ini tial and final quantum states is not small. Calculations are also perf ormed for the probability of resonant transfer of vibrational excitati on energy between molecules in clusters using a mixed quantum-classica l calculational procedure. It is found that quantum coherence effects are observed for several picoseconds in the probability for resonant t ransfer in these systems. (C) 1998 John Wiley & Sons, Inc.