A pulsed Lavai nozzle apparatus with laser ionization mass spectroscopy for direct measurements of rate coefficients at low temperatures with condensable gases

Abstract

A pulsed Lavai nozzle, low Mach number supersonic expansion kinetics apparatus has been constructed to study neutral-neutral kinetics by a rather general laser photolysis initiation and laser photoionization detection of the product species. This new apparatus permits laboratory studies of low temperature rate coefficients (e.g., 70-170 K) on condensable gases that have insufficient vapor pressures at low temperatures for conventional methods of kinetic measurements. The design considerations, the uniformity of the reaction zone over 10-20 cm, and the skimmer sampling of the pulsed Laval expansion are examined. The direct measurement of a rate coefficient at 90 K is also demonstrated using this new apparatus. © 2000 American Institute of Physics.