Vibrational Spectroscopy and Dynamics of Reaction Intermediates

宾夕法尼亚大学的玛莎·莱斯特在化学结构、动力学和机制项目的支持下开展了一系列化学反应动力学的基础实验研究，其中许多是基于大气中具有重要意义的化学系统。实验利用了最先进的光谱和动力学方法，但采用了独特的方法，从沿反应坐标的稳定中间体开始研究。具体来说，计划中的研究重点是OH和CN自由基与反应势能表面上的分子伴侣结合产生的弱结合物质。在这些研究中，CN自由基或中间体氢化物拉伸的基或泛音激发将提供足够的能量来启动反应势能表面上的动力学。实验可观察物包括表征反应中间体的光谱参数，例如分子结构、振动频率、解离和/或反应阈值。此外，从产物的内部和/或动能释放，得到中间产物的键能和生成焓，可以获得离解和/或反应动力学的动力学信息。实验结果将与由从头算势能面导出的类似性质的理论计算进行比较。在这个项目中，本科、研究生和博士后水平的年轻科学家将参与最前沿的科学研究，培养进入科技队伍所需的技能、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.