Dynamics of Electronically Excited States. Models for Chemical Reactivity

点击翻译按钮获取中文摘要

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.