Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH3)2COO

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• 作者：Rabi Chhantyal-Pun ; Oliver Welz ; John D. Savee ; Arkke J. Eskola ; Edmond P. F. Lee ; Lucy Blacker ; Henry R. Hill ; Matilda Ashcroft ; M. Anwar H. Khan ; Guy C. Lloyd-Jones ; Louise Evans ; Brandon Rotavera ; Haifeng Huang ; David L. Osborn ; Daniel K. W. Mok ; John M. Dyke ; Dudley E. Shallcross ; Carl J. Percival ; Andrew J. Orr-Ewing ; Craig A. Taatjes
• 刊名：Journal of Physical Chemistry A
• 出版年：2017
• 出版时间：January 12, 2017
• 年：2017
• 卷：121
• 期：1
• 页码：4-15
• 全文大小：602K
• ISSN：1520-5215

文摘

The Criegee intermediate acetone oxide, (CH<sub>3sub>)<sub>2sub>COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O<sub>2sub> and characterized by synchrotron photoionization mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO<sub>2sub> was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10<sup>–11sup> cm<sup>3sup> s<sup>–1sup> at 298 K and 4 Torr and (1.5 ± 0.5) × 10<sup>–10sup> cm<sup>3sup> s<sup>–1sup> at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of anti-CH<sub>3sub>CHOO with SO<sub>2sub>, and in good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 and 100 Torr) in N<sub>2sub> from cavity ring-down decay of the ultraviolet absorption of (CH<sub>3sub>)<sub>2sub>COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10<sup>–10sup> to (2.29 ± 0.08) × 10<sup>–10sup> cm<sup>3sup> s<sup>–1sup>. Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, k<sub>Hsub>/k<sub>Dsub> = (0.53 ± 0.06), for reactions with SO<sub>2sub>, which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD<sub>3sub>)<sub>2sub>COO with NO<sub>2sub> has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10<sup>–12sup> cm<sup>3sup> s<sup>–1sup> (measured with photoionization mass spectrometry), again similar to rate for the reaction of anti-CH<sub>3sub>CHOO with NO<sub>2sub>. Cavity ring-down measurements of the acetone oxide removal without added reagents display a combination of first- and second-order decay kinetics, which can be deconvolved to derive values for both the self-reaction of (CH<sub>3sub>)<sub>2sub>COO and its unimolecular thermal decay. The inferred unimolecular decay rate coefficient at 293 K, (305 ± 70) s<sup>–1sup>, is similar to determinations from ozonolysis. The present measurements confirm the large rate coefficient for reaction of (CH<sub>3sub>)<sub>2sub>COO with SO<sub>2sub> and the small rate coefficient for its reaction with water. Product measurements of the reactions of (CH<sub>3sub>)<sub>2sub>COO with NO<sub>2sub> and with SO<sub>2sub> suggest that these reactions may facilitate isomerization to 2-hydroperoxypropene, possibly by subsequent reactions of association products.