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Title:THE EFFECT OF SELECTIVE DEUTERATION ON MVK-OXIDE AND ITS UNIMOLECULAR DECAY TO HYDROXYL RADICAL PRODUCTS
Author(s):Liu, Ziao
Contributor(s):Lester, Marsha ; Hansen, Anne S
Subject(s):Atmospheric science
Abstract:The reaction of ozone with isoprene, one of the most abundant volatile organic compounds emitted into the atmosphere, produces three distinct carbonyl oxide species (R$_{1}$R$_{2}$COO) known as Criegee intermediates: formaldehyde oxide (CH$_{2}$OO), methyl vinyl ketone oxide (MVK-oxide), and methacrolein oxide (MACR-oxide). Unimolecular decay of MVK-oxide is predicted to be the major source of hydroxyl radicals (OH) derived from isoprene ozonolysis in the atmosphere. Previously, infrared (IR) action spectroscopy of \textit{syn}-MVK-oxide was shown to yield OH radical products following unimolecular decay via a 1,4-H transfer process\footnote{\textit{J. Am. Chem. Soc.} 2018, 140, 34, 10866-10880}. Here, we investigate the IR action spectroscopy and unimolecular decay of selectively deuterated MVK-oxide ($d_3$-MVK-oxide, \chem{(CH_2=CH)(CD_3)COO}) with deuterium atom transfer as the rate limiting step. The IR action spectrum of \textit{syn}-$d_3$-MVK-oxide is recorded in the CH stretch overtone (2$\nub{\textnormal{CH}}$) region with detection of OD products by laser-induced fluorescence. The temporal profile arising from unimolecular decay to OD products is also obtained. The experimental results are compared with the calculated IR absorption spectrum and the unimolecular decay rates predicted by Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The IR action spectrum shows two distinctive features in the 6100-6200 \wn region and two broad features from 5950 to 6050 \wn. The $d_3$-MVK-oxide IR action spectrum exhibits notable changes compared to MVK-oxide, as the overtone and combination transitions involving CD stretch shift to lower frequency, resulting in fewer transitions in this region. The unimolecular decay rate for MVK-oxide is predicted to be 100 times slower upon deuteration. Experimentally, a significantly slower appearance of OD products from $d_3$-MVK-oxide is found compared to OH products from MVK-oxide, indicating that tunneling plays a very important role in 1,4-H/D transfer. The similarities in the IR action spectra indicate that the \textit{syn} conformers make the main contribution to the observed spectra.
Issue Date:26-Jun-20
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/107619
Date Available in IDEALS:2020-06-26


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