Study of the kinetics of the reactions of NO3 with HO2 and OH

The Absolute rate constants for the gas-phase reactions of NO₃ with HO₂ and OH have been determined using the discharge flow laser magnetic resonance method (DF-LMR). Since OH was found to be produced in the reaction of HO₂ with NO₃, C₂F₃Cl was used to scavenge it. The overall rate constant, k₁, for the reaction, HO₂ + NO₃ → products, was measured to be k₁=(3.0 ± 0.7)×10^?12 cm³ molecule^?1 s^?1 at (297 ± 2) K and P=(1.4 – 1.9) torr. This result is in reasonable agreement with the previous studies. Direct detection of HO₂ and OH radicals and the use of three sources of NO₃ enabled us to confirm the existence of the channel producing OH:HO₂+NO₃→OH+NO₂+O₂ (1a); the other possible channel is HO₂+NO₃→HNO₃+O₂ (1b). From our measurements and the computer simulations, the branching ratio, k_1a/(k_1a + k_1b), was estimated to be (1.0). The rate coefficient for the reaction of OH with NO₃ was determined to be (2.1 ± 1.0) × 10^?11 cm³ molecule^?1 s^?1. © 1993 John Wiley & Sons, Inc.