The Role of Multiple Potential Energy Surfaces in Chemical Reactions and Photodissociation

马里兰大学帕克分校的米勒德·亚历山大和约翰·霍普金斯大学的保罗·达格迪吉安得到了实验物理化学计划的支持，继续他们对化学反应动力学和分子光解离的合作研究，重点是电子非绝热过程。理论研究涉及分子碰撞和解离动力学研究的新方法的发展和应用。这些实验将测量包括开壳硅藻在内的状态分辨的电子和旋转非弹性截面，特别关注光解制备的高激发转动能级。该项目的目标是阐明多个势能面之间的相互作用以及这些势能面之间的耦合如何控制反应截面和速率常数对反应物的精细结构水平的依赖，以及碰撞或光解后产物的内态分布和取向。这个项目的主要主题是电子角动量和/或自旋对化学反应、非弹性能量转移和光解的影响。通过对几个示范系统的研究，以及理论和实验的密切合作，实现了对充分理解的进展。自由基是具有不成对的电子自旋的原子和分子物种。这一性质导致它们具有化学反应活性，事实上，自由基反应是所有化学动力学的基础。涉及自由基的碰撞，以及导致自由基碎片的光诱导解离，都是复杂的过程，其描述本质上是量子力学的。这项工作旨在实现对自由基反应体系的基本了解，目的是提高对化学反应动力学和动力学的总体知识。

Millard Alexander of the University of Maryland at College Park and Paul Dagdigian of Johns Hopkins University are supported by the Experimental Physical Chemistry Program to continue their collaborative studies of the dynamics of chemical reactions and molecular photodissociation, with an emphasis on electronically nonadiabatic processes. The theoretical research involves the development and application of new methodology for the study of molecular collision and dissociation dynamics. The experiments will measure state-resolved electronically and rotationally inelastic cross sections involving open-shell diatomics, with special attention on highly excited rotational levels, photolytically prepared. The project goal is the elucidation of how the interplay between more than one potential energy surface, and the coupling between these, governs the dependence of reaction cross sections and rate constants on the fine-structure levels of the reactants, and product internal state distributions and orientation after collisions or photodissociation. The dominant theme of this project is the influence of electronic angular momentum and/or spin on chemical reactions, inelastic energy transfer and photodissociation. Progress toward full understanding is achieved by investigation of a few exemplary systems, with theory and experiment in close collaboration. Radicals are atomic and molecular species that have unpaired electron spins. This property leads them to be chemically reactive, and in fact radical reactions underlie all of chemical kinetics. Collisions that involve radicals, as well as light-induced dissociation that leads to radical fragments, are complex processes whose description is inherently quantum mechanical. This effort seeks to achieve fundamental understanding of radical reaction systems with the goal of improving overall knowledge of chemical reaction dynamics and kinetics.