The development of semiclassical dynamical methods and their application to vibrational relaxation in condensed-phase systems

A semiclassical surface-hopping propagator for problems involving nonadiabatic transitions is discussed. The propagator is employed in expressions for the probability of transitions between quantum states of molecules in condensed phases. This approach is implemented for the evaluation of the rate of vibrational transitions in liquids, dense gases, and clusters. Results for the rates of relaxation of excited vibrational 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 calculations on simple model systems. It is found that these simplifying approximations work well as long as the energy difference between the initial and final quantum states is not small. Calculations are also performed for the probability of resonant transfer of vibrational excitation energy between molecules in clusters using a mixed quantum-classical calculational procedure. It is found that quantum coherence effects are observed for several picoseconds in the probability for resonant transfer in these systems. (C) 1998 John Wiley & Sons, Inc.