Dynamics of Electronically Excited States. Models for Chemical Reactivity

实验物理化学计划支持匹兹堡大学的大卫·普拉特继续研究使用分子束中旋转分辨荧光激发光谱的范德华络合物的电子光谱。目标是a)确定最低两个单重态的苯-水络合物的分子间势能面，b)确定溶剂引起的甲苯胺-水络合物中肽键结构的变化，c)研究络合物形成对分子内弛豫过程的影响，以及4)研究化学反应动力学的构象控制。还将进行力场和从头计算。这些研究更具全局性的目标是研究从量子力学到经典极限的点，通过研究更大的非对称转子，通过激发到紫外线深处，具有更小的能级间距。物质在许多长度尺度上呈现出层次结构，在一个尺度上的“集合”在下一个尺度上变成了“组成部分”。在这个层级中，范德华相互作用和氢键扮演着特别重要的角色，导致孤立的分子聚集成组件，成为宏观液体和固体相的特征组成部分。在蛋白质、基因、膜和其他生命系统的大分子组成的复杂三维结构中，氢键也是一个普遍存在的特征。因此，重要的是要确定和表征构成微观和宏观领域之间的桥梁的基本“超分子”单元。这就是这些研究的目的。

The Experimental Physical Chemistry Program supports David Pratt from the University of Pittsburgh in his continuing studies of the electronic spectroscopy of van der Waals complexes using rotationally-resolved fluorescence excitation spectroscopy in molecular beams. The goals are to a) determine the intermolecular potential energy surfaces of the benzene-water complex in the lowest two singlet electronic states, b) determine the solvent-induced changes in the structure of the peptide bond in the formanilide-water complex, c) study the influence of complex formation on intramolecular relaxation processes, and 4) study conformational control of chemical reaction dynamics. Force field and ab initio calculations will also be carried out. The more global objective of these studies is to investigate the point at which one goes from the quantum mechanical to the classical limit, by studying larger asymmetric rotors with smaller energy level spacings via excitation deep into the ultraviolet. Matter exhibits a hierarchy of structures at many length scales, with `assemblies` at one scale becoming `component parts` at the next. In this hierarchy, van der Waals interactions and hydrogen bonding play particularly prominent roles, leading to the aggregation of isolated molecules into assemblies that become the characteristic component parts of macroscopic liquid and solid phases. Hydrogen bonding also appears as a ubiquitous feature in the complex three-dimensional structures of proteins, genes, membranes, and other macromolecular constituents of living systems. It is therefore important to identify and characterize the basic `supramolecular` units that form the bridge between the microscopic and macroscopic domains. This is the purpose of these studies.