title: Detailed mechanism of the CH₂I + O₂ reaction: yield and self-reaction of the simplest Criegee intermediate CH₂OO.
abstract: The application of a new reaction scheme using CH2I + O2 to generate the simplest Criegee intermediate, CH2OO, has stimulated lively research; the Criegee intermediates are extremely important in atmospheric chemistry. The detailed mechanism of CH2I + O2 is hence important in understanding kinetics involving CH2OO. We employed ultraviolet absorption to probe simultaneously CH2I2, CH2OO, CH2I, and IO in the reaction system of CH2I + O2 upon photolysis at 248 nm of a flowing mixture of CH2I2, O2, and N2 (or SF6) in the pressure range 7.6-779 Torr to investigate the reaction kinetics. With a detailed mechanism to model the observed temporal profiles of CH2I, CH2OO, and IO, we found that various channels of the reaction CH2I + O2 and CH2OO + I play important roles; an additional decomposition channel of CH2I + O2 to form products other than CH2OO or ICH2OO becomes important at pressure less than 60 Torr. The pressure dependence of the derived rate coefficients of various channels of reactions of CH2I + O2 and CH2OO + I has been determined. We derived a rate coefficient also for the self-reaction of CH2OO as k = (8 ± 4) × 10(-11) cm(3) molecule(-1) s(-1) at 295 K. The yield of CH2OO from CH2I + O2 was found to have a pressure dependence on N2 and O2 smaller than in previous reports; for air under 1 atm, the yield of ~30% is about twice of previous estimates.
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Wei-Lun
authors.initials: WL
authors.lastname: Ting
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Chun-Hung
authors.initials: CH
authors.lastname: Chang
authors.affiliation: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan.
authors.forename: Yu-Fang
authors.initials: YF
authors.lastname: Lee
authors.affiliation: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Matsui
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Yuan-Pern
authors.initials: YP
authors.lastname: Lee
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Jim Jr-Min
authors.initials: JJ
authors.lastname: Lin