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

在本研究计画中，我一直在研究质子在冰中的传递、液体的高阶非线性光谱、液态水的冻结机制。本文用QM/MM方法分析了冰中质子快速转移（PT）的势能面和反应坐标沿着PT。在冰中，H_3O^+与周围分子的四种相互作用中有一种是排斥作用，因此不能发生大的结构变化，如氧原子之间的距离缩小。这两个关键因素导致在冰中沿沿着PT的小能量势垒。因此，冰中PT是快速的，尽管PT在冰中的详细机理与在液体中有很大的不同.液体的高阶非线性光谱我们用“广义量子主方程”分析了重质HDO的一维和二维红外光谱。在该方法中，溶剂的波动被适当地考虑在HDO分子的振动态的密度矩阵的动力学。因此，可以分析凝聚相中的任何类型的振动弛豫和振动光谱。基于分子动力学模拟，研究了液态CS_3的二维拉曼信号.分子液体的液-固相变我们用恒温恒压分子动力学方法分析了Stockmayer流体和液态水的液-固相变。在水的计算中也采用了多正则蒙特卡罗和副本交换方法。

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.