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]/[O 2] = 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 H 2-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) cm3mol -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) cm3mol-1. S-t. 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.