Measurement of the rate coefficient for the reaction of O(1D) with H2O and re-evaluation of the atmospheric OH production rate

The rate coefficient for the reaction of O(1D) with H2O (Reaction 1), whose value is critical for calculating production rates of the OH radical in the atmosphere, was measured over a range of atmospherically relevant temperatures. The temporal profile of O(3P) following photolytic production of O(1D) in the presence of water vapor was used to determine a temperature dependent value for k1 of (1.45 ± 0.34) × 10−10 exp((89 ± 65)/T) cm3 molecule−1 s−1, where the quoted errors are at the 95% confidence level, include estimated systematic errors and σA = AσlnA. In addition, ratios of rate coefficients for quenching of O(1D) by N2 and O2 (k2 and k3) to that for Reaction 1 were determined to be k2/k1 = (0.13 ± 0.04) and k3/k1 = (0.19 ± 0.09) by measuring the relative OH concentration produced from Reaction 1 in the presence of various concentrations of N2 or O2. Combining our results of this work with previous measurements of k1, we recommend a value for k1 = (1.62 ± 0.27) × 10−10 exp((65 ± 50)/T) cm3 molecule−1 s−1, where the quoted errors are 95% confidence level, include estimated systematic errors and σA = AσlnA. Based on these results, the uncertainty in the calculated atmospheric OH production rate due to the uncertainty in these rate coefficients is reduced from ±50% to ±20%.