Initiation in H2/o2: Rate Constants for H2 O2 → H Ho2 at High Temperature

The reaction between H2 and O2 has been studied in a reflected shock tube apparatus between temperatures of 1662–2097 K and pressures of 400–570 torr with Kr as the diluent gas. O atom atomic resonance absorption spectrometry (ARAS) was used to observe absolute [O]t under conditions of low [H2]0 so that most secondary reactions were negligible. Hence, the observed [O]t was the direct result of the rate controlling reaction between H2 and O2. Three different reactions were considered, but experimental and ab initio theoretical results both indicated that the process, H2 O2 → H HO2, is the most probable reaction. After rapid HO2 dissociation, O atoms are then instantaneously produced by H O2 → O OH. Using the ab initio result, conventional transition state theoretical calculations (CTST) with tunneling corrections give the expression T2.4328 exp( 26,926 K/T) cm3 molth 18 k 1.228 10 1 ecule 1 s 1, applicable between 400 and 2300 K. This theoretical result agrees with the present experimental determinations and those at lower temperature, derived from earlier work on the reverse reaction.