| This thesis considers the mechanisms by which molecular dynamics in nonpolar liquids influences solvation dynamics and vibrational energy relaxation.; We use semiclassical molecular dynamics simulations to calculate photon echo signals for two simple fluids. We demonstrate that two new observables are directly related to the relevant molecular quantity, the frequency-frequency time correlation function (TCF), in contrast to the commonly measured 3PEPS, which cannot be simply related to this TCF at short times. We also present a semianalytic photon echo theory, based on an ansatz which determines the full time dependence from the short time expansion coefficients of the TCF. We demonstrate that this theory accurately predicts most photon echo observables, even when the theory's gaussian approximation is not accurate.; We also consider vibrational energy relaxation (VER) in liquid oxygen. Using semiclassical molecular dynamics simulations and an intermolecular potential from the literature, we evaluate the required quantity (the spectral density of a certain force-force TCF) using the same ansatz described above. We demonstrate numerically that this procedure is accurate. Approximately relating this semiclassical rate to the fully quantum mechanical VER rate, using one of the more accurate “quantum corrections” available in the literature, yields a result which is in order-of-magnitude agreement with the experimental VER rate.; We also calculate the VER rate for liquid oxygen/argon mixtures. The rotations of the solvent near a vibrationally excited molecule, and of that molecule itself, have important consequences for the short-time dynamics of the force-force TCF. We propose a simple statistical model which quantitatively explains the mole-fraction dependence of the observed VER rate.; Next, we demonstrate that a newly-developed model for oxygen very accurately describes the liquid, by comparing to experimental measures of microscopic structure and dynamics. We also demonstrate that if the dependence of the intermolecular potential on vibrational coordinate is considered, this new model qualitatively predicts both the isotropic Raman line width and lineshape along the liquid-gas coexistence curve. The calculated VER rate for this new model is in quantitative agreement with experiment. |
