KINETICS AND TEMPERATURE-DEPENDENCE OF THE BRO + CLO REACTION

The kinetics of the BrO + ClO reaction was studied over the temperature range 234-406 K by discharge flow/mass spectrometry. The total rate constant for the reaction was found to have a significant negative activation energy and is given by k(l) (T) = (2.59 +/- 0.36) x 10(-12) exp[(445 +/- 84)/T] cm3 molecule-1 s-1. The reaction has three product channels: (a) ClOO + Br, (b) OClO + Br, and (c) BrCl + O2. The branching ratios for the three channels as a function of temperature were measured, and it was found that the channel leading to formation of OClO becomes dominant at lower temperatures (branching ratio of 0.51 at 250 K). Evidence for the direct formation of BrCl was found, yielding a branching ratio of 0.09-0.10 for the BrCl channel over the temperature range 250-406 K. The temperature-dependent rate coefficients for the three channels are given by k1a = (2.1 +/- 0.4) x 10(-12) exp[(258 +/- 56)/T], k1b = (6.7 +/- 1.0) x 10(-13) exp[(622 +/- 94)/T], and k1c = (1.9 +/- 0.6) x 10(-13) exp[(513 +/- 86)/T] cm3 molecule-1 s-1. These results are discussed relative to other recent studies and their importance in understanding the stratospheric chemistry of the Antarctic ozone hole.