Vibrational Spectroscopy and Dynamics of Reaction Intermediates

宾夕法尼亚大学的玛莎·莱斯特得到了化学结构、动力学和机制计划的支持，开展了一系列化学反应动力学的基础实验研究，其中许多研究是基于大气中具有重要意义的化学系统。这些实验利用了最先进的光谱和动力学方法，但采用了一种独特的方法，即从位于反应坐标上的稳定中间体开始研究。具体地说，计划中的研究集中在OH和CN自由基与反应势能面上的分子伙伴缔合产生的弱结合物种。在每一项研究中，CN自由基或中间体的氢化物伸展的基音或泛音激发将提供足够的能量来启动反应势能面上的动力学。实验观测包括高细节地表征反应中间体的光谱参数，例如分子结构、振动频率和解离和/或反应的阈值。此外，有关解离和/或反应动力学的动力学信息将从内部和/或向产物的动能释放中获得，从而产生中间体的键能和生成热。实验结果将与从头算势能面得到的类似性质的理论计算进行比较。在这个项目中，本科生、研究生和博士后级别的年轻科学家将参与前沿科学研究，培养进入科学技术大军所需的技能、经验和信心。参与者--其中许多是女性--在从事基础研究项目时使用了技术先进的激光设备，这些项目也与大气化学中更广泛的问题有关。

Marsha Lester of the University of Pennsylvania is supported by the Chemical Structures, Dynamics and Mechanisms program to carry out a series of fundamental experimental studies of chemical reaction dynamics, many of which are based on chemical systems of significance in the atmosphere. The experiments utilize state-of-the-art spectroscopic and dynamical methods, but with the unique approach of initiating the studies from stabilized intermediates that lie along the reaction coordinate. Specifically, the planned studies focus on weakly bound species produced by association of OH and CN radicals with molecular partners on reactive potential energy surfaces. In each of these studies, fundamental or overtone excitation of the CN radical or hydride stretch of the intermediate will provide sufficient energy to initiate dynamics on a reactive potential energy surface. Experimental observables include spectroscopic parameters that characterize the reaction intermediates in high detail, for example molecular structures, vibrational frequencies, and thresholds for dissociation and/or reaction. In addition, dynamical information on dissociation and/or reaction dynamics will be obtained from the internal and/or kinetic energy release to products, yielding bond energies and enthalpies of formation for the intermediates. Experimental outcomes will be compared with theoretical calculations of the analogous properties derived from ab initio potential energy surfaces.In this project, young scientists at the undergraduate, graduate, and postdoctoral levels will participate in forefront scientific research, developing skills, experience, and confidence required to move into the scientific and technical workforce. The participants -- many of whom are women -- use technologically advanced laser equipment as they work on basic research projects, which are also relevant to broader issues in atmospheric chemistry.