Semiclassical theory and simulation of vibrational energy relaxation and spectroscopic response functions in liquids

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Professor Eitan Geva is supported by the Theoretical and Computational Chemistry Program to understand the quantum dynamics of liquid solutions. This requires one to focus on quantities that are used to probe the structure and dynamics of liquid solutions and leads to consideration of two primary problems. The first problem requires a new approach for calculating the vibrational energy relaxation rate constants in liquids. These rate constants are very sensitive to quantum dynamics and are important for understanding solute-solvent interactions. The second major component of the research deals with the calculation of optical response functions, which provide a means for probing solvation dynamics. To computationally determine vibrational energy relaxation rates a new method, based on linear response theory, is being developed and applied. The advantage of this method is it bypasses the need for calculating the high-frequency part of the Fourier transform of the force-force correlation function. The research employs an idealized model consisting of two-level chromophores, an anharmonic nonpolar solvent, solute-solvent interactions that vary with the chromophore electronic state and a dipolar interaction between the field and matter. A complementary senior-level undergraduate training program in modern computational chemistry is included that aims to bring together computational scientists from disparate disciplines and foster cross-departmental collaborations. Applications of this method are applied to successively more complex dimer/solvent systems and progress from neutral homonuclear diatomics to neutral heteronuclear diatomics and finally to charged homonuclear diatomics. The advent of ultrafast lasers has led to a multitude of novel techniques that enable the direct interrogation of solvation dynamics. Such experiments effectively allow one to experimentally unlock mechanisms occurring at the femtosecond time scale and should provide a new means for understanding biologically relevant processes. However, access to this information comes in the form of photon echoes, nature's analogy to the Morse code, and necessitates new theoretical techniques for correctly determining what the encoded echoes are telling us. The goal of this research is to develop and apply a new theoretical approach that decodes the information contained in the outgoing light. Initial applications are on a class of dimer/solvent systems for which there is a good amount of experimental data and which systematically contain all the electrostatic complications that are present in nonpolar solutions containing larger molecules. A senior level undergraduate course is being developed which will provide future graduate students with tools required for theoretical physical chemistry.