SPECTROSCOPIC CHARACTERIZATION OF AN ALKYL-SUBSTITUTED CRIEGEE INTERMEDIATE CH$_{3}$CHOO AND ITS OH RADICAL PRODUCTS

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2013

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Ohio State University

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In the atmosphere, cycloaddition of ozone to the double bond of alkenes produces energized Criegee intermediates, which undergo subsequent decay processes to yield OH radicals. In this laboratory, a simple alkyl-substituted Criegee intermediate CH$_{3}$CHOO is produced by 248 nm photolysis of CH$_{3}$CHI$_{2}$ and subsequent reaction of CH$_{3}$CHI with O$_{2}$ in a quartz capillary tube reactor, following the same approach utilized for CH$_{2}$OO., 20045 (2012).} The CH$_{3}$CHOO intermediate (m/z=60) and other products are detected following supersonic expansion using 118 nm VUV ionization in a time-of-flight mass spectrometer. The OH radical products from decomposition of the CH$_{3}$CHOO intermediate are also directly detected at m/z=17 using a new UV+VUV ionization scheme, combining UV excitation on the OH A ^2$\Sigma^+$-X ^2$\Pi$ (1,0) transition with fixed-frequency VUV at 118 nm,, 241102 (2011).} or alternatively by UV laser-induced fluorescence on the OH A-X transition; OH products are also observed from CH$_{2}$OO. The CH$_{3}$CHOO intermediate is characterized by a strong B $^1$A$^\prime$-X $^1$A$^\prime$ electronic transition, in which UV excitation near the peak of a broad absorption profile centered at 320 nm results in significant depletion of the CH$_{3}$CHOO photoionization signal. The mechanism proposed for OH generation from energized CH$_{3}$CHOO and many larger Criegee intermediates is a 1,4 H-atom shift to form vinylhydroperoxide species that decay to produce OH. This reaction scheme provides a non-photolytic source of OH radicals in the atmosphere during night and winter times.

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Author Institution: Department of Chemsitry, University of Pennsylvania, Philadelphia, PA 19104-6323

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