J Phys Chem Lett. 2025 Nov 4:11770-11776. doi: 10.1021/acs.jpclett.5c02949. Online ahead of print.
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 archetype 1Br– + 1O3 reaction, which proceeds with an experimental rate constant of 8.9 (±4.4) × 10-15 cm3 molecule-1 s-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 yield 1BrO– + 3O2. Statistical rate modeling using this new barrier height predicts a rate constant of 5.7 × 10-15 cm3 molecule-1 s-1, which is in excellent agreement with the experiment. This reconciliation of the kinetics for the intrinsic gas-phase reaction will enable systematic evaluation of temperature, pressure, and solvation effects on this ion-molecule chemistry and thus inform the impact of halide anion chemistry on atmospheric ozone.
PMID:41186043 | DOI:10.1021/acs.jpclett.5c02949
