Theoretical and Experimental Study of Electronic Non- adiabaticity in Molecular Collisions and Photofragmentation

本项目由化学学部物理化学项目资助，马里兰大学的亚历山大和约翰霍普金斯大学的达迪吉安将进行理论与实验的联合研究，以确定分子的能量状态是如何影响分子碰撞和光解离的。特别是，由于分子能态很少是理论公式初始阶段使用的理想的、独立的状态，它们之间的相互作用在确定碰撞和光解过程的细节方面起着重要作用。几种典型的自由基分子，包括二原子和三原子单氢化物，将被研究。这个项目的理论部分（M. Alexander）涉及发展新的方法来阐明分子碰撞和光解离的机制。实验部分（P. Dagdigian）包括确定分子经历能量变化的非弹性碰撞的横截面。还需要确定的是由母体分子光解作用产生的分子片段的内能态分布。分子能量主要被认为是平动、旋转、振动和电子运动的结果，而电子运动由轨道和自旋贡献组成。然而，在分子结构和动力学的概念模型中，将总能量分离为独立的贡献只是理想的第一步，为了解释观察到的分子性质，允许这些运动之间的相互作用是必要的。分子间的光解离和碰撞也受到这些相互作用的影响，这在开壳（自由基）分子中尤为明显。在本研究中进行的调查将有助于理解这些过程，并将有助于确定关于开壳分子的基本Born-Oppenheimer近似的有效性限制。

In this project, supported by the Physical Chemistry Program of the Chemistry Division, Profs. M. Alexander of the University of Maryland and P. Dagdigian of Johns Hopkins University will pursue a joint theoretical-experimental effort to determine how molecular collisions and photodissociations are affected by molecular energy states. In particular, since molecular energy states are rarely the idealized, independent states used in the initial stages of theoretical formulations, the interactions between them play a signifant role in determining the details of the collision and photodissociation processes. Several prototypical free radical molecules, including di-and triatomic monohydride species, will be investigated. The theoretical portion of this project (M. Alexander) involves the development of new methods to elucidate the mechanism of molecular collisions and photodissociation. The experimental portion (P. Dagdigian) involves the determination of cross sections for inelastic collisions in which molecules undergo energy changes. Also to be determined are the distributions over the internal energy states of a molecular fragment that results from the photodissociation of the parent molecule. %%% Molecular energies are considered in the main to be the result of translational, rotational, vibrational and electronic motions, with the latter being made up of orbital and spin contributions. This separation of the total energy into independent contributions is, however, only an idealized first step in the conceptual model of molecular structure and dynamics, and allowing for interactions between these motions is necessary in order to account for the observed molecular properties. Photodissociations and collisions between molecules are also affected by these interactions, which are particularly evident in open shell (free radical) molecules. The investigations to be carried out in this research will contribute to the understanding of these processes and will assist in establishing the limits of validity of the fundamental Born-Oppenheimer approximation to open shell molecules.