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

点击翻译按钮获取中文摘要

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.