Theoretical Study of Chemical Reactions in solution and Higher Order Nonlinear Spectroscopies

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In this research project, I have been investigating proton transfer in ice, higher order nonlinear spectroscopies of liquids, and freezing mechanism of liquid water.1. Fast Proton Transfer (PT) in IceWe have analyzed potential energy surface and reaction coordinate along PT in ice by using a QM/MM method. In ice, one of four interactions between H_3O^+ and surrounding molecules is repulsive and a large structure change such as a shrinkage of distance between oxygen atoms cannot take place. These two crucial elements result in a small energy barrier along PT in ice. Therefore, PT in ice is fast, though the detailed mechanism of PT in ice is quite different from that in liquid.2. Higher Order Nonlinear Spectroscopies of LiquidsWe have analyzed one- and two-dimensional infrared spectroscopies of HDO in heavy by using 'generalized Quantum Master equation'. In the method, solvent fluctuations are properly considered in the dynamics of the density matrix of the vibrational states of a HDO molecule. Thus, it is possible to analyze any kinds of vibrational relaxation and vibrational spectroscopies in condensed phases. Two-dimensional Raman signal of liquid CS_3 is also investigated based on molecular dynamics simulation.3. Liquid-Solid Phase Transition of Molecular LiquidsWe have analyzed the liquid-solid phase transitions of a stockmayer fluid and liquid water by using a constant temperature and constant pressure molecular dynamics. Multicanonical monte carlo and replica exchange methods are also employed in the calculation of water.