Vibrational Spectroscopy and Relaxation in Liquids and Supercritical Fluids

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James Skinner of the University of Wisconsin, Madison, is supported by the Theoretical and Computational Chemistry Program to develop a general framework within which to calculate time- and frequency-domain vibrational spectra of solutes in liquid solvents. This approach builds on the work of others, where the solute and vibrational degrees of freedom are treated quantum mechanically, and the solute's rotations and translations and all solvent degrees of freedom are treated classically. The framework involves renormalization of the solute vibrations by the average interactions with the solvent, and so is expected to be able to describe systems with strong solute-solvent interactions. The theoretical approach will be applied to the following systems for which experiments have been performed: 1) HOD in liquid D2O (vibrational spectroscopy of the OH stretch), 2) the azide anion in liquid D2O (phonon vibrational spectroscopy of the azide anion asymmetric stretch), and 3) supercritical fluid oxygen and nitrogen (Raman spectroscopy). Finally, some general issues involving vibrational energy relaxation of solutes in polyatomic liquid solvents will be investigated.Many industrially and biologically important chemical reactions take place in liquid solution. The presence of solvent molecules are around a solute molecule can greatly affect rates and mechanisms of chemical reactions by changing the relative energy levels and providing pathways for efficient energy flow into and out of the solvent. This research project aims to provide a molecular level interpretation of the influence a solvent has on chemical and biological processes in condensed phases.