Kinetics of the Gas Phase Reactions of the Criegee Intermediate CHOO with O and IO.

The kinetics of the gas phase reactions of the Criegee intermediate CHOO with O and IO have been studied at 296 K and 300 Torr through simultaneous measurements of CHOO, the CHOO precursor (CHI), O, and IO using flash photolysis of CHI/O/O/N mixtures at 248 nm coupled to time-resolved broadband UV absorption spectroscopy. Experiments were performed under pseudo-first-order conditions with respect to O, with the rate coefficients for reactions of CHOO with O and IO obtained by fitting to the observed decays of CHOO using a model constrained to the measured concentrations of IO. Fits were performed globally, with the ratio between the initial concentration of O and the average concentration of IO varying in the range 30-700, and gave = (3.6 ± 0.8) × 10 cm molecule s and = (7.6 ± 1.4) × 10 cm molecule s (where the errors are at the 2σ level). The magnitude of has a significant effect on the steady state concentration of CHOO in chamber studies. Atmospheric implications of the results are discussed.