A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy

Rabi Chhantyal-Pun, Anthony Davey, Dudley E Shallcross, Carl J Percival, Andrew J Orr-Ewing

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Abstract

Criegee intermediates are important species formed during the ozonolysis of alkenes. Reaction of stabilized Criegee intermediates with various species like SO2 and NO2 may contribute significantly to tropospheric chemistry. In the laboratory, self-reaction can be an important loss pathway for Criegee intermediates and thus needs to be characterized to obtain accurate bimolecular reaction rate coefficients. Cavity ring-down spectroscopy was used to perform kinetic measurements for various reactions of CH2OO at 293 K and under low pressure (7 to 30 Torr) conditions. For the reaction CH2OO + CH2OO (8), a rate coefficient k8 = (7.35 ± 0.63) × 10(-11) cm(3) molecule(-1) s(-1) was derived from the measured CH2OO decay rates, using an absorption cross section value reported previously. A rate coefficient of k4 = (3.80 ± 0.04) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the CH2OO + SO2 (4) reaction. An upper limit for the unimolecular CH2OO loss rate coefficient of 11.6 ± 8.0 s(-1) was deduced from studies of reaction (4). SO2 catalysed CH2OO isomerization or intersystem crossing is proposed to occur with a rate coefficient of (3.53 ± 0.32) × 10(-11) cm(3) molecule(-1) s(-1).

Original languageEnglish
Pages (from-to)3617-3626
Number of pages10
JournalPhysical Chemistry Chemical Physics
Volume17
Issue number5
Early online date22 Dec 2014
DOIs
Publication statusPublished - 7 Feb 2015

Bibliographical note

Accepted 22/12/2014

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