Rate constants of HO2+NO covering atmospheric conditions .1. HO2 formed by OH+H2O2

Rate constants of the gas-phase reactions HO2 + NO --> products (1), HO2 + NO --> OH + NO2 (1a), and OH + NO --> products (2) were determined at room temperature and total pressures of 10, 50, and 100 kPa of N-2. OH radicals were produced by pulsed 248 nm photolysis of H2O2 and monitored by time-resolved CW UV-laser long-path absorption. Biexponential OH decay curves, observed in the presence of H2O2 and NO, were analyzed to obtain rate constants for the above reactions. Those of reactions 1 and 1a were found to be independent of pressure with averaged values of (9.7 +/- 1.5) x 10(-12) and (9.6 +/- 1.5) x 10(-12) cm(3) s(-1), respectively. This indicates an OH yield very close to unity (greater than or equal to 0.95) for the title reaction under the experimental conditions of this work. Error limits are estimated considering statistical and possible systematic errors. The pressure dependence found for reaction 2 is in good agreement with literature data. Rate constants of (1.3 +/- 0.4) x 10(-12), (4.7 +/- 0.8) x 10(-12), and (7.4 +/- 1.3) x 10(-12) cm(3) s(-1) have been determined for total pressures of 10, 50, and 100 kPa of N-2, respectively. Addition of H2O at mixing ratios of 1.7% had no influence on the investigated reactions, Moreover, a quantum yield less than or equal to 0.05 is estimated for the formation of H + HO2 in the 248 nm photolysis of H2O2. The rate constants of the HO2 + NO reaction are slightly larger (15%) than the most recent recommendations.