Kinetics of the HO2+BrO reaction over the temperature range 233–348 K

Abstract

The reaction BrO+HO ₂ →products is the rate-limiting step in a key catalytic ozone destruction cycle in the lower stratosphere. In this study a discharge-flow reactor coupled with molecular beam mass spectrometry has been used to study the BrO+HO ₂ reaction over the temperature range 233–348 K. Rate constants were measured under pseudo-first-order conditions in separate experiments with first HO ₂ and then BrO in excess in an effort to identify possible complications in the reaction conditions. At 298 K, the rate constant was determined to be (1.73±0.61)×10 ^-11 cm ³ molecule ^-1 s ^-1 with HO ₂ in excess and (2.05±0.64)×10 ^-11 cm ³ molecule ^-1 s ^-1 with BrO in excess. The combined results of the temperature-dependent experiments gave the following fit to the Arrhenius expression: k=(3.13±0.33)×10 ^-12 exp(536±206/T) where the quoted uncertainties represent two standard deviations. The reaction mechanism is discussed in light of recent ab initio results on the thermochemistry of isomers of possible reaction intermediates.