This project is in the general area of analytical and surface chemistry and in the subfields of photochemistry and surface reaction dynamics. The research continues the Principal Investigator's studies of the photofragmentation, via internally repulsive states excited by an ultraviolet laser, of molecules adsorbed on metal and semiconductor surfaces. Photofragmentation, which generates radicals important in surface reactions, can proceed on these surfaces even in the presence of very fast (250 - 2500 femtoseconds) quenching of the excited states by energy transfer to the substrate. The role of faster charge transfer processes (5 - 50 fs) will be investigated by measuring the cross- sections, photofragment velocity and angular distributions, and polarization dependence for a series of small adsorbate molecules. Ultraviolet laser surface photochemistry is an important new area of fundamental research which has potentially broad applications in diverse technological fields such as semiconductor processing, solar energy conversion, chemical catalysis, and eye surgery. However, little is known about the fundamental mechanisms underlying the photochemical reactions. Both charge transfer and electron attachment have been identified as important reaction channels. Studies of the photofragmentation of adsorbed molecules will provide a highly specific probe of the dynamics of energy and charge transfer at interfaces.
