DESIGN AND CHARACTERIZATION OF PULSED UNIFORM SUPERSONIC EXPANSIONS FOR CHEMICAL APPLICATIONS

A general formalism is presented for the production, characterization, and use of uniform supersonic flows for the study of structural and collisional molecular properties. These flows make possible the generation of thermally equilibrated gaseous environments at temperatures generally extending from near 10 to above 300 K at pressures between 0.1 and 10 Torr. In addition, the invariance of flow conditions for distances of many nozzle diameters (5-30) beyond the exit makes the flows ideal for collisional or temporal studies. A concise outline for the design of the Laval nozzles necessary to produce specified density and temperature conditions is presented. Pulsed operation of these expansions is demonstrated, and a variety of useful characterization tools providing information on flow uniformity and thermal characteristics is considered. Recent applications of these flows for the study of low-temperature chemical reactions are reviewed. (C) 1995 American Institute of Physics.