Resonant excitation transfer of molecular vibrations and time-domain optical processes in liquids and proteins

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Analysis of vibrational modes with large vibrational interactions is important for structural chemistry of large-size molecular systems such as proteins and liquids. It is expected that deep insight is obtained by analyzing phenomena related to those modes. The following studies have been carried out in relation to this point. (1) To clarify the factors that determine the intensities of the signals of time-domain optical processes, the effects of molecular hyperpolarizabilities on the low-frequency Raman and optical Kerr effect intensities of molecular liquids are examined. (2) A theoretical method is developed for analyzing the effect of liquid dynamics on the noncoincidence effect of Raman bands that arises from resonant excitation transfer of molecular vibrations in liquids. By using this method, an analysis is carried out for a real liquid system as an example. The changes in the vibrational eigenstates of the liquid on the sub-picosecond time scale arising from its dynamics are clarified in detail. (3) The interactions between vibrational modes with large dipole derivatives and nonpolar solvents are analyzed to get deep insight into the mechanism of vibrational dephasing that competes with resonant excitation transfer of molecular vibrations in liquids. It is shown that rather strong electric field exists around some widely used nonpolar solvent molecules such as carbon tetrachloride, and it arises from electric quadrupoles on the heavy atoms such as chlorine. (4) The concentration dependence of the noncoincidence effect of the Raman bands of the liquid mixtures of methanol and carbon tetrachloride is analyzed. It is shown that microscopically anisotropic structural changes occur as methanol is diluted in carbon tetrachloride. (5) The changes in the optical properties arising from the interactions between protein backbone and the dye molecule contained in it are analyzed. The role of vibrational modes with large vibrational interactions is shown.