Direct rate measurements on the reactions N + OH ? NO + H and O + OH ? O2+ H from 250 to 515 K

Abstract

Rate coefficients for the reactions N + OH → NO + H (1) and O + OH → O2+ H (2) have been determined, in direct experiments, from 250 to 515 K. A discharge-flow system is used to generate measured concentrations of N or O; then OH radicals are formed by flash photolysis of H2O and monitored by resonance fluoresence as they are removed by reaction (1) or (2) under pseudo-first-order conditions. The results are fitted to the rate expressions: k1=(2.21 ± 0.18)×10–10T–0.25 ± 0.17 cm3 molecule–1 s–1, k2=(6.65 ± 0.23)×10–10T–0.50 ± 0.12 cm3 molecule–1 s–1 where the errors represent 95% confidence intervals within the range of temperature covered in the experiments. The rate coefficient k2 is compared with a calculation assuming that the reaction proceeds via a bound state HO2 collision complex.