Collision-Induced Electronic Energy Transfer in Small Molecules (Chemistry)

达格迪吉安博士计划与马里兰大学的米勒德·亚历山大博士合作，继续一个理论与实验相结合的项目，研究小分子和自由基中的电子非弹性碰撞过程。这些实验将涉及使用光学-光学双共振来确定流动系统中具有初始和最终量子态分辨率的能量传递速率常数。将研究以下碰撞过程：(A)氮的低位三重态之间的跃迁，(B)CN和一氧化碳正离子的低位态之间的跃迁，(C)CS中的自旋变化跃迁，以及(D)一卤化钙激发态之间的跃迁。这项实验工作是与下列理论项目联合进行的：(A)发展电子非弹性碰撞的全量子描述，特别是那些涉及分子伙伴自旋多重数变化的碰撞，(B)确定与电子激发的CN和N的碰撞有关的从头算势能面和波函数，以及(C)基于从头算势面计算全态分辨截面。目前正在特别注意电子非绝热矩阵元素的计算，这些矩阵元素描述了碰撞伙伴的核运动与其组成电子的运动之间的耦合。这项研究很重要，因为所研究的过程负责分子的电子激发态的猝灭，以及许多化学发光反应中光子产额的压力依赖性。例如，长期以来，人们一直有兴趣了解控制包含电子激发氮分子的系统中能量流动的详细机制。由于它是我们大气的主要组成部分，因此关于氮的碰撞过程的知识对于理解极光和气辉等现象至关重要。在实验室中，氮通常存在于放电中的混合气体中，包括各种气体激光介质。

Dr. Dagdigian, in collaboration with Dr. Millard Alexander of the University of Maryland, plans to continue a joint theoretical-experimental project involving studies of electronically inelastic collision processes in small molecules and radicals. The experiments will involve the use of optical-optical double resonance for the determination of energy transfer rate constants with initial and final quantum state resolution in a flow system. The following collisional processes will be investigated: (a) transitions between low-lying triplet states of nitrogen, (b) transitions among low-lying states of CN and carbon monoxide positive ions, (c) spin-changing transitions in CS, and (d) transitions between excited states of the calcium monohalides. This experimental work is being carried out jointly with the following theoretical projects: (a) the development of the fully quantum description of electronically inelastic collisions, in particular those involving a change in spin multiplicity of the molecular partner, (b) the determination of ab initio potential energy surfaces and wavefunctions relevant to collisions of electronically excited CN and nitrogen, and (c) the calculation of fully state-resolved cross sections based on ab initio potential surfaces. Specific attention is being given to the calculation of the electronically nonadiabatic matrix elements which describe the coupling between the nuclear motion of the collision partners and the motion of their constituent electrons. This research is important because the processes under investigation are responsible for quenching of electronically excited states of molecules and for the pressure dependence of photon yields in many chemiluminescent reactions. For example, there has been a long-standing interest in understanding the detailed mechanisms that govern energy flow in systems containing electronically excited nitrogen molecules. Since it is the major component of our atmosphere, knowledge about collisional processes of nitrogen is crucial for an understanding of phenomena such as auroras and airglows. In the laboratory, nitrogen is often present in gas mixtures in discharges, including various gas laser media.