Kinetics of the Gas Phase Reactions of the Criegee Intermediate CH2OO with O3 and IO.

Abstract

The kinetics of the gas phase reactions of the Criegee intermediate CH2OO with O3 and IO have been studied at 296 K and 300 Torr through simultaneous measurements of CH2OO, the CH2OO precursor (CH2I2), O3, and IO using flash photolysis of CH2I2/O2/O3/N2 mixtures at 248 nm coupled to time-resolved broadband UV absorption spectroscopy. Experiments were performed under pseudo-first-order conditions with respect to O3, with the rate coefficients for reactions of CH2OO with O3 and IO obtained by fitting to the observed decays of CH2OO using a model constrained to the measured concentrations of IO. Fits were performed globally, with the ratio between the initial concentration of O3 and the average concentration of IO varying in the range 30-700, and gave kCH2OO+O3 = (3.6 ± 0.8) × 10-13 cm3 molecule-1 s-1 and kCH2OO+IO = (7.6 ± 1.4) × 10-11 cm3 molecule-1 s-1 (where the errors are at the 2σ level). The magnitude of kCH2OO+O3 has a significant effect on the steady state concentration of CH2OO in chamber studies. Atmospheric implications of the results are discussed.