The Short-Time Dynamics of Liquids

理查德·斯特拉特，布朗大学，由理论与计算化学项目资助，继续他在液体短时间动力学方面的理论研究。Stratt试图根据液体振动的瞬时正模（INS）理论，解释最近从溶剂化动力学的随时间斯托克斯位移测量以及纯液体的傅立叶变换拉曼（光学克尔效应）光谱中获得的光谱数据。需要开展的两个基本不同的研究方向是：1)探索INS分析协助超快光谱实验解释的方法；2)找到将可行时间范围尽可能扩展到非线性状态的方法，并发现该技术的真正极限在哪里。非线性的影响将通过检查时间演变来研究，既通过精确模拟，也通过某种更解析的方式，将非线性形式化地视为扰动。人们所认为的化学过程中有很大一部分是在溶液中发生的，而在液体环境中的化学过程通常与分子完全分离的情况下的化学过程看起来大不相同。这些差异的起源是什么，以及这些差异究竟是如何从溶剂的分子性质中产生的，这些问题一直是每一代新光谱技术反复追求的问题。最近在阐明液体中线性激励概念方面的理论进展表明，用一组液体振动（即所谓的液体的瞬时正常模式）控制的液态的短时间演化来思考可能确实是有用的。Stratt研究的主要目的是看看这个理论结构是否可以解释最近从超快光谱中获得的结果，并提供分子水平上对液体状态的结构和动力学的解释。

Richard Stratt, Brown University, is supported by a grant from the Theoretical and Computational Chemistry Program to continue his theoretical research in the short time dynamics of liquids. Stratt seeks to interpret recent spectroscopic data obtained from time-dependent-Stokes-shift measurements of solvation dynamics as well as Fourier transform Raman (Optical Kerr effect) spectra of neat liquids in terms of the instantaneous normal mode (INS) theory of the liquid vibrations. Two fundamentally disparate research directions to be undertaken are: 1) to explore the ways in which INS analysis can assist in the interpretation of ultrafast spectroscopic experiments; and 2) to find ways of extending the workable time span into the nonlinear regime as much as possible, and to discover where the true limits of the technique lie. The effects of nonlinearity will be studied by examining the time evolution, both via exact simulation and somewhat more analytically, by considering the nonlinearity formally as a perturbation. A significant fraction of what one thinks about as chemistry takes place in solution, and chemical processes often look far different in a liquid environment than they would if the molecules were completely isolated. Just what the origins of these differences are, and precisely how these distinctions arise from the molecular properties of the solvent are questions that have been pursued repeatedly with each new generation of spectroscopic technique. Recent theoretical progress in elucidating the concept of linear excitations in liquids suggests that it may indeed be useful to think in terms the short time evolution in the liquid-state being governed by a set of liquid vibrations -- the so-called instantaneous normal modes of the liquid. The major purpose of Stratt's research is to see if this theoretical construct can lead to interpretation of recent results obtained from ultrafast spectroscopy, and to provide a molecular level interpretation of the structure and dynamics of the liquid state.