Study of the kinetics of the reactions of NO 3 with HO 2 and OH

The Absolute rate constants for the gas‐phase reactions of NO 3 with HO 2 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 HO 2 with NO 3 , C 2 F 3 Cl was used to scavenge it. The overall rate constant, k 1 , for the reaction, HO 2 + NO 3 → products, was measured to be k 1 =(3.0 ± 0.7)×10 −12 cm 3 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 HO 2 and OH radicals and the use of three sources of NO 3 enabled us to confirm the existence of the channel producing OH:HO 2 +NO 3 →OH+NO 2 +O 2 (1a); the other possible channel is HO 2 +NO 3 →HNO 3 +O 2 (1b). From our measurements and the computer simulations, the branching ratio, k 1a /( k 1a + k 1b ), was estimated to be (1.0   −0.3 +0.0 ). The rate coefficient for the reaction of OH with NO 3 was determined to be (2.1 ± 1.0) × 10 −11 cm 3 molecule −1 s −1 . © 1993 John Wiley & Sons, Inc.