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Published August 21, 1997 | Published
Journal Article Open

Kinetics of the HO_2 + 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) x 10^(-11) cm^3 molecule^(-1) s^(-1) with HO_2 in excess and (2.05 ± 0.64) x 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.

Additional Information

© 1997 Royal Society of Chemistry. Received 6th March, 1997. This research was performed by the Jet Propulsion Laboratory, California Institute Technology, under contract with National Aeronautics and Space Administration. We are grateful to J. S. Francisco and S. Guha for providing details of their ab initio calculations on HBrO and to David Natzic 3, and Juergen Linke for their expert technical assistance in this work.

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