The Development of Semiclassical Methods for the Evaluation of Vibrational Energy Relaxation Rates in Condensed Media

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Michael Herman, Tulane University, is supported by a grant from the Theoretical and Computational Chemistry Program to continue his theoretical work on the development of semiclassical methods for the evaluation of vibrational relaxation rates in condensed media. The goal of this work is the development of well tested, accurate methods that are sufficiently flexible so as to allow for the evaluation of the vibrational energy relaxation in a broad range of physical systems. The strategies for the development of these methods employ a quantum mechanical description of the vibrational motion of the molecules. Semiclassical techniques are employed to describe the time evolution of the nonvibrational degrees of freedom in the system. These methods allow for the coupling of the evolution of the nonvibrational degrees of freedom to the quantum vibrational transitions, while retaining much of the computational advantage of a classical mechanical description. The rate at which molecules gain and lose vibrational energy influences reaction kinetics, energy transport, the interpretation of spectroscopic experiments and many other processes occurring in liquids, dense gases and solids. The theoretical description of this problem, in a manner that leads to quantitative predictions, requires that the vibrations be treated quantum mechanically. The evaluation of transition rates between quantum states of the molecule in a condensed phase system is an important and challenging theoretical problem, requiring the coupling of quantum techniques with procedures for averaging over the multitude of configurations available to the condensed phase system.