Rate constants for the reaction, O+H 2O→OH+OH, over the temperature range, 1500–2400 K, by the flash photolysis-shock tube technique: A further consideration of the back reaction

Abstract

Rate constants for the reaction, O+H 2 O→OH+OH, have been measured by the Flash Photolysis-Shock Tube (FP-ST) technique over the temperature range, 1500–2400 K. This technique combines shock heating with flash photolysis in the reflected shock wave regime, and the transient species, O-atoms in this case, are monitored by atomic resonance absorption spectroscopy (aras). Additional experiments were performed with N 2 O as a thermal source of O-atoms, and the formation and depletion of [O] were followed by the aras technique. These results require that the decomposition rate behavior of N 2 O be known. The results obtained by this technique are compared to those obtained by the FP-ST technique and are found to be corroborative. Hence, the combined results are used to describe the rate constants for the title reaction. These results can be represented by the Arrhenius expression: k =(1.12±0.20)×10 −10 exp(−9115±304 K/T) cm 3 molecule −1 s −1 over the experimental temperature range. The individual data points deviate from this equation by ±17% at the one standard deviation level, and this represents a measure of the precision. The experimental results are compared to earlier work, and rate constants for the title reaction are additionally calculated from published results for the reverse reaction, OH+OH, and the well known equilibrium constant. All results are combined, and the rate behavior for the title reaction is evaluated. The three parameter expression is, k =8.44×10 −14 T 0.946 exp(−8571 K/T) cm 3 molecule −1 s −1 for the temperature range, 250–2400 K. Lastly, the results for both forward and reverse reactions are compared to the theoretical calculations presented recently by Harding and Wagner. It is concluded that theory and experiment are in agreement within experimental error.