Proton Transfer Dynamics in Water and Effect of Water Fluctuation on Chemical Reactions

水中质子传递动力学及水波动对化学反应的影响

基本信息

批准号：
08404040
负责人：
OHMINE Iwao
金额：
$ 24.26万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

项目摘要

Various aspects of Water Dynamics were analyzed ; (1) Fluctuation and Relaxation in Liquid Water and their Observation, (2) Proton Transfer in Liquid Water and Ice, (3) Solvation Dynamics in Supercritical Water, and (4) Mechanism of Water Freezing.(1) Water has the rugged potential energy surface involving various deep energy minima with different hydrogen bond network structures. Water undergoes the sluggish dynamics on this potential energy surface. In a short time scale liquid water is thus amorphous gel-like, while in a very longer time scale it exhibits diffusional motion as an ordinal liquid. In between these time scales, the hydrogen bond network rearrangement occurs intermittently and locally in space, involving the local collective motions of tens of water molecules accompanied with the large energy fluctuation. The various experimental techniques to observe the effects of intermittent collective motions in water are discussed. Particular emphasis is on the higher-order nonlin … More ear specutroscopies since these methods deal with the phase-space dynamics of a system. There have been intensive theoretical investigations proposing to apply the echo-type experiment, i.e. the off-resonant fifth order (two-dimensional (2D) Raman) spectroscopy to distinguish the homogeneous and the inhomogeneous elements in liquid dynamics.(2) Proton transfer in water is assisted by Hydrogen Bond Network Rearrangement (HBNR), making some water molecules three-coordinated. Proton transfer takes place on these three-coordinated water molecules. On the other hand, the protonated water molecule is four-coordinated in ice, but its interaction with the fourth coordinated water molecule is repulsive (while those with first three are attractive) ; four-coordinated geometrically and three-coordinated energetically. Due to this repulsive interaction with the fourth water molecule, 0-- (H) --O distances with the other three water molecules become short and thus facile proton transfer can take place even in ice without causing a significant HBNR.^2(3) We also analyze the mechanism of the water molecule dissociation. A water molecule dissociates to H^+ and OH (ionic channel) in liquid water. In the gas phase, however, water is known to separate into two radicals, H and OH.This radical channel is about 290 kcal/mol more stable than the ionic channel. In water the ion channel is extensively stabilized by hydration and thus water yields pH = 7. It is also found that in super-critical water the hydration is stronger than in water in spite of the fact that water molecular density is smaller, and hence the ionic channel becomes even more stable.(4) We have investigated the freezing mechanism of liquid water was investigated by using molecular dynamics simulation. Placing a small ice-structured unit in a center of a simulation box, the processes of forming an well-ordered hydrogen bond network around it were monitored. It was found that crystallization suddenly takes place after certain induction-time. Various analyses were made to find how the hydrogen bond network grows in this freezing mechanism. Less

分析了水动力学的各个方面。（1）在液态水中的波动和放松，（2）液体水和冰中的质子转移，（3）超临界水中的溶剂化动力学，（4）水冷冻机理。（1）水具有坚固的势能表面，涉及具有不同氢键网络结构的各种深度能量最小值。水在这种势能表面上经历了缓慢的动态。因此，在短时间内，液态水是无定形的凝胶状的，而在较长的时间尺度上，液态水作为顺序液体表现出差异运动。在这些时间尺度之间，氢键网络重排在空间中间歇性地发生，涉及几十水分子的局部集体运动，并伴随着大能量波动。讨论了观察水中间歇性集体运动影响的各种实验技术。特别强调的是高阶非林…更多的早期光谱镜，因为这些方法涉及系统的相位动力学。已经进行了深入的理论研究，该研究提议应用回声型实验，即抗谐振的第五顺序（二维（2D）拉曼）光谱范围，以区分液体动力学中的均匀元素和均匀元素。质子转移发生在这三配合的水分子上。另一方面，质子化的水分子在冰中是四协调的，但它与第四个协调的水分子相互作用是令人反感的（而前三个具有吸引力的人）；从几何和三协调的基本上是四协调的。由于与第四水分子的排斥相互作用，0-（h） - 与其他三个水分子的距离变得较短，因此即使在冰中也可以在冰中进行柔和的质子转移。^2（3），我们还分析了水分子解离的机制。水分子在液态水中分离为H^+和OH（离子通道）。但是，在气相中，已知水分为两个自由基H和OH。该自由基通道比离子通道更稳定约290 kcal/mol。在水中，离子通道通过水分进行了广泛的稳定，因此水产生pH = 7。尽管水分子密度较小，因此在超临界水中，水合比在水中强，因此离子通道变得更加稳定。在模拟盒的中心放置一个小的冰结构单元，监测形成有序的氢键网络的过程。发现结晶突然发生在一定的诱导时间之后。进行了各种分析，以找到在这种冰点机制中如何增长的氢键网络。较少的