Theoretical Studies of Intramolecular Dynamics and Energy Redistribution

Citation

Voth, Gregory Alan (1987) Theoretical Studies of Intramolecular Dynamics and Energy Redistribution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MD4H-AZ79. https://resolver.caltech.edu/CaltechETD:etd-11292006-135710

Abstract

By virtue of various theoretical techniques, the fundamental mechanisms responsible for intramolecular vibrational energy redistribution (IVR) in isolated molecules are studied in this thesis. One such mechanism, the nonlinear resonance, is examined in some detail for several systems. In particular, nonlinear stretch-bend resonances in a series of isotopically substituted methanes are predicted to have a large effect on the spectral properties of those molecules. By using a semiclassical analysis, the general properties of stretch-bend interactions are further examined, and the quantum mechanical manifestations of classical resonances are characterized in detail. A related problem, the role of classical resonances in the multiphoton absorption process by an anharmonic oscillator, is also analyzed.

In addition, it is demonstrated that the quantum mechanical coupled equations which describe the fundamental IVR process may be simplified. This simplification is achieved by virtue of an "adiabatic" approximation for those state amplitudes which are sufficiently off-resonant with (i.e., different in energy from) the experimentally prepared quantum state. The approximate coupled equations are based on an effective Hamiltonian which contains renormalized self-energies and interactions between the zeroth-order quantum states. This formalism may be applied to describe the quasidissipative flow of probability out of an initially prepared vibrational state in a large molecule, and it may also be adapted to treat multiphoton absorption processes in polyatomic molecules when one or more lasers are present.

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