Kinetics and mechanism of the OH + HO₂ reaction

A discharge flow reactor with laser magnetic resonance and resonance fluorescence detection axes is used to measure the rate constant for the reaction of OH and HO₂ radicals by measuring the decay of OH in excess HO₂ under pseudo-first-order conditions. Particular care is taken to reduce impurity O and H atoms to low levels since their presence leads to an underestimate of the rate constant. The rate constant is measured to be (8.0_-2.0^+3.0) × 10^-11 cm³ molecule^-1 s^-1 at 298 K and 2 Torr after a small (3%) correction is made for the impurity atoms. It is argued that recent experimental and theoretical results indicate that the reaction mechanism is likely dominated by attack at the hydrogen end of HO₂ and that the reaction is unusually fast due a long-range attractive interaction.