Studying Intermolecular Interactions and Bimolecular Reactions Through van der Waals Complexes

在化学学部实验物理化学项目的这个项目中，宾夕法尼亚大学的H.L. Dai将研究分子间的相互作用，如电子能量转移和通过范德华络合物的双分子反应。本研究包括几个部分：用激光诱导荧光光谱法研究范德华配合物中碰撞诱导的电子弛豫过程；乙二醛、嘧啶等分子电子弛豫中的分子轨道依赖性及不同碰撞伙伴的影响以及电子激发分子的化学反应，或者在范德华复合体中被激发到选定振动水平的分子。范德华振动模式的结构和频率将通过荧光激发和受激发射光谱来确定。这些结果将用于测试计算分子间电位的理论模型。这项研究处理的问题是能量如何在振动和电子激发的分子内部和分子之间流动。所研究的分子被纳入分子簇中，这些分子簇通过弱分子间的范德华力结合在一起。组分分子的振动或电子激发通常会使复合物解离。这种解离过程模拟了发生在碰撞分子之间的能量转移。在范德华复合体中嵌入分子的实验提供了一种控制反应过程的方法，这是分子具有随机取向的分子气体所无法实现的。这些实验将为理解不同分子轨道的反应性和确定表征反应的势能面提供有用的信息。有了这些信息，就有可能设计出新的光化学反应途径。

In this project in the Experimental Physical Chemistry Program of the Chemistry Division, H.L. Dai of the University of Pennsylvania will investigate intermolecular interactions such as electronic energy transfer and bimolecular reactions through van der Waals complexes. The study consists of several parts,namely investigation of collision induced electronic relaxation processes in van der Waals complexes by means of laser induced fluorescence spectroscopy; molecular orbital dependence in the electronic relaxation of molecules like glyoxal and pyrimidene and the effect of different collision partners; and the chemistry of electronically excited molecules, or molecules excited to selected vibrational levels in a van der Waals complex. The structure and frequencies of the van der Waals vibrational modes will be determined by means of fluorescence excitation and stimulated emission spectroscopy. These results will be used to test theoreticel models for calculating intermolecular potentials. %%% This research deals with the problem of how energy flows within and among vibrationally and electronically excited molecules. The molecules of study are incorporated in molecular clusters which are held together by weak intermolecular van der Waals forces. Vibrational or electronic excitation of the component molecules will generally cause the complex to dissociate. This dissociation process mimics the energy transfer that occurs between colliding molecules. The experiments with molecules embedded in a van der Waals complex provide a measure of control over the reaction process that is not available with molecular gases in which the molecules have random orientation. The experiments will provide information useful for the understanding of the reactivity of different molecular orbitals, and for the determination of the potential energy surface which characterizes the reaction. With this information it will be possible to devise novel photochemical reaction pathways.