Recombination in the hydrogen-oxygen reaction: A shock tube study with nitrogen and water vapour as third bodies

Abstract

Previous shock tube studies of termolecular recombination in the hydrogen-oxygen reaction have been extended to mixtures containing significant amounts of nitrogen or water vapour. An OH ultra-violet line absorption technique has been used to follow the progress of the overall reaction at temperatures of 1259° to 1912°K and pressures of 1·1 to 3·7 atm. Selective variation of the initial composition, which for the water vapour experiments required the development of a special flow-fill apparatus to introduce up to 7·9 per cent water vapour into the unshocked gas mixtures, has made possible a determination of the effect of both of these species as third bodies on the three important recombination reactions: H + H + M → H 2 + M H + O 2 + M → H O 2 + M H + O H + M → H 2 O + M . Results in mixtures diluted with nitrogen indicate that the rate coefficient of each of these reactions with the third body M = N 2 are approximately 1·5 times the values previously reported for M = Ar. Determination of the water vapour coefficients is complicated by the presence of other important third bodies, i.e. argon and hydrogen or oxygen. However, the results show that water vapour is an efficient catalyst in bringing about recombination. The ratio of rate coefficients for M = H 2O to those with M = Ar for these three reactions is ⩽ 13.25, and 20, respectively.