Time-Resolved Structural Studies of Reacting Molecules Using Stroboscopic Gas Electron Diffraction Synchronous with Photoexcitation

在化学系物理化学项目的这个项目中，阿肯色大学化学系的J. Ewbank和L. Schafer教授将继续将频闪衍射技术应用于化学反应的结构动力学。激光激发的气相分子将使用时间分辨电子散射进行研究，以提供有关反应分子结构和振动概率分布的时间演化信息。时间分辨率将扩展到皮秒时域，并将用于研究紫外线诱导的不饱和有机化合物（如反式二苯乙烯）异构化，以及红外多光子吸收诱导的过程（如分子内振动能量重新分配和解离反应）的结构和分布动力学。对非平衡分布中带电分子结构动力学的实验观察是一个重要的化学前沿，它将刺激理论的进步。传统的气体电子衍射（GED）依赖于利用照相底片来记录和存储分子衍射电子所产生的信息。因此，这种方法仅限于研究稳定分子的结构。当前分子动力学的研究关注的是在化学反应过程中分子系统的结构和构象是如何演变的。关于这些过程的实验信息只能通过以时间为主要因素的技术来获得。由主要研究人员开发的实时GED方法为了解短寿命物种的性质做出了重要贡献。该项目的目的是利用这一潜力，并有助于我们对分子动力学的基本方面的理解。

In this project in the Physical Chemistry Program of the Chemistry Division, Professors J. Ewbank and L. Schafer of the Chemistry Department of the University of Arkansas will continue to apply stroboscopic diffraction techniques to the structural dynamics of chemical reactions. Laser-excited molecules in the vapor phase will be studied using time-resolved electron scattering in order to provide information about the time evolution of structures and vibrational probability distributions in reacting molecules. The time resolution will be extended down to the picosecond time domain and will be used to study UV-induced isomerizations of unsaturated organic compounds such as trans-stilbene, and structural and distribution dynamics following IR multiphoton absorption-induced processes such as intramolecular vibrational energy redistribution and dissociation reactions. Experimental observations of the structural kinetics of energized molecules in non-equilibrium distributions are an important chemical frontier which will stimulate advances in theory. Traditional gas electron diffraction (GED) has relied on the use of the photographic plate to record and store the information generated by the diffraction of electrons by molecules. This method was therefore limited to studying the structures of stable molecules. Current research in molecular dynamics concerns itself with how the structure and conformation of a molecular system evolves during a chemical reaction. Experimental information about such processes can be obtained only by means of techniques in which the time plays an essential role. The method of real-time GED developed by the principal investigators has shown great promise in making important contribution to the understanding of the properties of short-lived species. The aim of this project is to capitalize on this potential and contribute to our understanding of the basic aspects of molecular dynamics.