Electronic Nonadiabaticity in Chemical Dynamics

马里兰大学帕克分校的米勒德·h·亚历山大和约翰·霍普金斯大学的保罗·j·达迪吉安得到了实验物理化学计划的支持，继续他们对涉及双原子自由基的非反应性碰撞动力学的合作研究，重点是电子非绝热过程。他们将研究自由基的弱结合配合物和这些配合物的预解离，以便获得有关潜在势能表面的进一步信息。理论方面的工作包括开发和应用新的方法来阐明分子碰撞和光解离的机制，从头计算势能面和非绝热耦合矩阵元素，全量子计算截面和速率常数，以及确定弱结合配合物的弯曲拉伸水平。实验工作包括确定能量传递过程的状态到状态非弹性截面以及稀有气体-双原子范德华配合物的光谱和动力学。他们研究的主要主题是电子角动量和/或自旋对非弹性能量传递和光解的影响。在碰撞或分子分裂过程中，内部电子角动量将与原子核的运动耦合，从而影响产物分支比和非弹性倾向。因此，对这种耦合机制的透彻理解将最终导致对如何优化化学反应中所需产物的更好理解。

Millard H. Alexander of The University of Maryland at College Park and Paul J. Dagdigian of Johns Hopkins University are supported by the Experimental Physical Chemistry Program to continue their collaborative studies of the dynamics of nonreactive collisions involving diatomic free radicals, with an emphasis on electronically nonadiabatic processes. They will study weakly bound complexes of the radicals and the predissociation of these complexes in order to gain further information on the underlying potential energy surfaces. The theoretical effort involves development and application of new methods for elucidating the mechanism of molecular collisions and photodissociation, ab initio calculation of the potential energy surfaces and nonadiabatic coupling matrix elements, and full quantum calculations of cross sections and rate constants and the determination of bend-stretch levels of weakly-bound complexes. The experimental effort involves the determination of state-to-state inelastic cross sections for energy transfer processes and the spectroscopy and dynamics of rare gas-diatomic van der Waals complexes. The dominant theme of their research is the influence of electronic angular momentum and/or spin on inelastic energy transfer and photodissociation. During a collision, or during the breakup of a molecule, the internal electronic angular momenta will couple with the motion of the nuclei and hence influence product branching ratios and inelastic propensities. Therefore, a thorough understanding of this coupling mechanism should ultimately lead to a better understanding of how to optimize the desired products in chemical reactions.