Rate constant for the reaction Br + O₃ → BrO + O₂ from 248 to 418 K: Kinetics and mechanism

The rate constant for the Br + O 3 → BrO + O 2 reaction was measured by the discharge flow technique, employing resonance fluorescence detection of Br. Over the temperature range 248 to 418 K, in 1 to 3 torr of He, decays of Br in excess O 3 yield the value k 1 = (3.28 ± 0.40) × 10 −11 e [−944±30]/ T cm 3 molecule −1 s −1 . Cited uncertainties are at the 95% confidence level and include an estimate of the systematic errors. The rate constants for the reactions of O 3 with Br, Cl, F, OH, O, and N correlate with the electron affinities of the radicals suggesting that the reactions proceed through early transition states dominated by transfer of electron density from the highest occupied molecular orbital of ozone to the singly occupied radical MO. The implications of this new measurement of k 1 for stratospheric chemistry are discussed.