With support from the Experimental Physical Chemistry Program, Mark Smith of The University of Arizona is continuing his studies on the kinetics of low temperature reactions. In the past, he has used resonance-enhanced multiphoton ionization detection to study (a) collisions of neutral molecules or radicals in a free jet at very low temperatures, and (b) radical reactions in a pulsed equilibrium axisymmetric supersonic flow reactor (Laval nozzle) between 80 and 250K. Next, he will extend the free jet studies by incorporating single-state preparation and/or state-selective probes. He will also continue his investigations of the 60-300K chemistry of hydroxyl radicals, chlorine atoms and other reactive oxygen-containing radicals with a variety of atmospherically relevant reactants. Broad based investigations will be made into the mechanism and dynamics of gas phase chemical reactions at temperatures between 300 and 1K. The primary goals of this work include the refinement of the developing understanding of very low energy collision phenomena as well as the provision of absolute reaction rates and product branching ratios. Such measurements are critically needed for the modeling of planetary atmospheric, cometary, circumstellar and interstellar chemical environments.
