Photometric determination of the rate of H 2O formation from H and OH in the presence of phosphine combustion products

Abstract

Laser photolysis experiments are reported in which gas-phase H 2O at 1960 K is photolyzed to H and OH radicals and the rate of recombination is measured. Previously, the rate of net H + OH recombination was determined by photometric measurements of OH radicals. In this article, photometric measurements at 192 nm, where H 2O absorbs at elevated temperatures, are reported. When small quantities of PH 3 combustion products are present in the test gas mixture, the rate of relaxation of the system to its initial state is increased substantially. A reaction model previously used to analyze OH kinetic data satisfactorily describes the time evolution of the H 2O signal. These results confirm the hypothesis that phosphine combustion products open new channels for recombination of H and OH that compete with the three-body recombination reaction, H + OH + M → H 2O + M.