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

Abstract

The reaction BrO+HO₂→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+HO₂ reaction over the temperature range 233–348 K. Rate constants were measured under pseudo-first-order conditions in separate experiments with first HO₂ 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 cm³ molecule^-1 s^-1 with HO₂ in excess and (2.05±0.64)×10^-11 cm³ 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.

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