Halving the Barrier to Gas-Phase Oxidation of Bromide by Ozone

Abstract

Recent atmospheric measurements indicate that bromine and iodine may be responsible for up to 72% of halogen-induced ozone loss near the tropopause, yet there is ongoing uncertainty regarding the multiphase chemistry of bromide and iodide anions in ozone depletion. Here, we demonstrate the unequivocal ozone-dependence of the archetype1Br–+1O3reaction, which proceeds with an experimental rate constant of 8.9 (±4.4) × 10–15cm3molecule–1s–1. The reaction mechanism is revised to proceed via a singlet transition state with a rate-limiting barrier of +22.1 kJ mol–1−half that of prior estimates −prior to facile spin-crossing to yield1BrO–+3O2. Statistical rate modeling using this new barrier height..