Temperature and pressure dependence of the rate constant for the HO2 + NO reaction

The rate constant for the reaction HO2 + NO → OH + NO2 has been measured using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. At room temperature, the rate constant was found to be independent of pressure between 70 and 190 Torr of N2 and given by (8.0 ± 0.5) × 10-12 cm3 molecule-1 s-1. The temperature dependence of the rate constant was investigated between 206 and 295 K; the Arrhenius expression over this temperature range is (3.0 ± 0.4) × 10-12 exp[(290 ± 30)/T] cm3 molecule-1 s-1. The uncertainties of the room temperature rate constant and the Arrhenius parameters represent the precision of the data and are reported at the 1 standard deviation level. We estimate that possible systematic errors limit the accuracy of the determined rate constants to ±15%. Comparison of our data with the results of previous studies indicates that the rate constant for the HO2 + NO → OH + NO2 reaction does not depend on the inert gas pressure for 295 K ≥ T ≥ 206 K