Rate constant of OH + OH = H2O + O from 1500 to 2000 K

Abstract

It was shown several years ago that concentration profiles of the OH radical in the shock-initiated combustion of lean ([H2]/[O2] = 0.1) hydrogen-oxygen-argon mixtures at low pressures (≃ 30 kPa) and high temperatures (1200–2000 K) exhibit transient maxima prior to attainment of partial equilibrium. At that time, the maxima could not be accounted for quantitatively in terms of the accepted mechanism of the H2–O2 reaction. The profiles have been reanalyzed utilizing more sophisticated computational techniques and increased knowledge of the reaction mechanism. The occurrence of maxima at temperatures above 1500 K was found to depend upon the ratio of the rate constants of the elementary reactions O+H2→OH+H and OH+OH→H2O+O. Using the rate constant expression 1.6×1014 exp(−56.6 kJ/R T) cm3 mol−1 s−1 for the former reaction, the rate constant expression for the latter was found to be 5.5×1013 exp(−29 kJ/R T) cm3 mol−1 s−1. This latter expression does not extrapolate linearly on an Arrhenius plot to the available room temperature data. The effect of boundary layer growth on the data analysis is discussed.