Theoretical Study on fluctuations in condensed phases and nonlinear spectroscopies

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In this study, we have investigated fluctuations in condensed phases ; multidimensional vibrational spectroscopy, phase transition dynamics of water, and chamical reactions in supercritical water.We have been theoretically investigating two-dimensinal (2D) Raman spectroscopy of liquids. As a two-dimensional NMR method, the multidimensional vibrational spectroscopies provide detailed information on dynamics that canot be obtained in conventional Raman spectroscopies. It was found that there exist changes in sign near the second time variable t_2 in the 2D Raman signals calculated with molecular dynamics simulation. The changes in sign are not seen in the signals based on normal mode descriptions. Thus it was found that they are related to anharmonic dynamics of the system. Various analyses have been made to understand what kind of dynamics is seen in the 2D Raman signals of liquid CS_2. We have found that a rotation-rotation dynamical coupling is the dominant contribution of the 2D Raman signal of liquid CS_2. The temperature dependence of the 2D Raman signal has been analyzing.We have analyzed the melting process of ice by using molecular dynamics simulations. It was found that the melting is followed by disorders of hydrogen bond network in the ice. We have analyzed the dynamics of translational and rotational motions and density fluctuation in the melting process.The dissociation of formic acid in a sub- and super-critical water has been also investigated.