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J Phys Chem A

Title:		Experimental Evidence of Dioxole Unimolecular Decay Pathway for Isoprene-Derived Criegee Intermediates
Author(s):		Vansco MF; Caravan RL; Zuraski K; Winiberg FAF; Au K; Trongsiriwat N; Walsh PJ; Osborn DL; Percival CJ; Khan MAH; Shallcross DE; Taatjes CA; Lester MI;
Address:		"Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States. NASA Postdoctoral Program, NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, United States. Combustion Research Facility, Sandia National Laboratories, Mailstop 9055, Livermore, California 94551, United States. Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States. NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, United States. California Institute of Technology, Pasadena, California 91125, United States. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K"
Journal Title:		J Phys Chem A
Year:		2020
Volume:		20200422
Issue:		18
Page Number:		3542 - 3554
DOI:		10.1021/acs.jpca.0c02138
ISSN/ISBN:		1520-5215 (Electronic) 1089-5639 (Linking)
Abstract:		"Ozonolysis of isoprene, one of the most abundant volatile organic compounds emitted into the Earth's atmosphere, generates two four-carbon unsaturated Criegee intermediates, methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide). The extended conjugation between the vinyl substituent and carbonyl oxide groups of these Criegee intermediates facilitates rapid electrocyclic ring closures that form five-membered cyclic peroxides, known as dioxoles. This study reports the first experimental evidence of this novel decay pathway, which is predicted to be the dominant atmospheric sink for specific conformational forms of MVK-oxide (anti) and MACR-oxide (syn) with the vinyl substituent adjacent to the terminal O atom. The resulting dioxoles are predicted to undergo rapid unimolecular decay to oxygenated hydrocarbon radical products, including acetyl, vinoxy, formyl, and 2-methylvinoxy radicals. In the presence of O(2), these radicals rapidly react to form peroxy radicals (ROO), which quickly decay via carbon-centered radical intermediates (QOOH) to stable carbonyl products that were identified in this work. The carbonyl products were detected under thermal conditions (298 K, 10 Torr He) using multiplexed photoionization mass spectrometry (MPIMS). The main products (and associated relative abundances) originating from unimolecular decay of anti-MVK-oxide and subsequent reaction with O(2) are formaldehyde (88 +/- 5%), ketene (9 +/- 1%), and glyoxal (3 +/- 1%). Those identified from the unimolecular decay of syn-MACR-oxide and subsequent reaction with O(2) are acetaldehyde (37 +/- 7%), vinyl alcohol (9 +/- 1%), methylketene (2 +/- 1%), and acrolein (52 +/- 5%). In addition to the stable carbonyl products, the secondary peroxy chemistry also generates OH or HO(2) radical coproducts"
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Notes:		"PubMed-not-MEDLINEVansco, Michael F Caravan, Rebecca L Zuraski, Kristen Winiberg, Frank A F Au, Kendrew Trongsiriwat, Nisalak Walsh, Patrick J Osborn, David L Percival, Carl J Khan, M Anwar H Shallcross, Dudley E Taatjes, Craig A Lester, Marsha I eng 2020/04/08 J Phys Chem A. 2020 May 7; 124(18):3542-3554. doi: 10.1021/acs.jpca.0c02138. Epub 2020 Apr 22"