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Photochem Photobiol

Title:		Insights into the Ultrafast Photodissociation Dynamics of Isoprene-Derived Criegee Intermediates
Author(s):		Antwi E; Packer NA; Ratliff JM; Marchetti B; Karsili TNV;
Address:		"University of Louisiana at Lafayette, Lafayette, LA, USA"
Journal Title:		Photochem Photobiol
Year:		2023
Volume:		20221123
Issue:		4
Page Number:		1072 - 1079
DOI:		10.1111/php.13736
ISSN/ISBN:		1751-1097 (Electronic) 0031-8655 (Linking)
Abstract:		"Isoprene is the most abundant nonmethane volatile organic compound emitted into the troposphere by terrestrial vegetation. Reaction with ozone represents an important isoprene removal process from the troposphere and is a well-known source of Criegee intermediates (CIs), which are reactive carbonyl oxides. Three CIs, formaldehyde oxide (CH(2) OO), methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide) are formed during isoprene ozonolysis. All three CIs contain strongly absorbing pipi* states, electronic excitation, which leads to dissociation to form aldehyde/ketone + oxygen products. Here, we compare the excited state chemistry of CH(2) OO, MVK-oxide and MACR-oxide in order to ascertain how increasing molecular complexity affects their photodynamics. In CH(2) OO, vertical excitation to the S(2) state leads to prompt O-O bond fission with a unity quantum yield. Branching into both the O ((1) D) + H(2) CO (S(0) ) and O ((3) P) + H(2) CO (T(1) ) product channels is predicted, with 80% of trajectories dissociating to form the former product pair. Analogous vertical excitation of the lowest energy conformers of MVK-oxide and MACR-oxide also undergoes O-O bond fission to form O + MVK/MACR products-albeit with a nonunity quantum yield. In the latter case, ca. 10% and 25% of trajectories remain as the parent MVK-oxide and MACR-oxide molecules, respectively. Additionally, at most only 5% of the dissociating trajectories form O ((3) P) + MVK/MACR (T(1) ) products, with a greater fraction forming O ((1) D) + MVK/MACR (S(0) ) products (cf. CH(2) OO). This latter observation coupled with the greater fraction of undissociated trajectories aligns with the bathochromic shift in the electronic absorption of the MACR-oxide and MVK-oxide (cf. CH(2) OO). We discuss the implications of the results in a broader context, including those that are relevant to the atmosphere"
Keywords:
Notes:		"PubMed-not-MEDLINEAntwi, Ernest Packer, Niamh A Ratliff, Jordyn M Marchetti, Barbara Karsili, Tolga N V eng 2003422/National Science Foundation/ 2022/10/30 Photochem Photobiol. 2023 Jul-Aug; 99(4):1072-1079. doi: 10.1111/php.13736. Epub 2022 Nov 23"