UV spectroscopic characterization of an alkyl substituted Criegee intermediate CH3CHOO

Beames, Joseph ORCID: https://orcid.org/0000-0002-5508-8236, Liu, Fang, Lu, Lu and Lester, Marsha I. 2013. UV spectroscopic characterization of an alkyl substituted Criegee intermediate CH3CHOO. Journal of Chemical Physics 138 (24) , 244307. 10.1063/1.4810865

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Abstract

Ozonolysis of alkenes in the troposphere proceeds through a Criegee intermediate, or carbonyl oxide, which has only recently been detected in the gas phase. The present study focuses on the production of an alkyl-substituted Criegee intermediate, CH3CHOO, in a pulsed supersonic expansion, and then utilizes VUV photoionization at 118 nm and UV-induced depletion of the m/z = 60 signal to probe the B 1A′ ← X 1A′ transition. The UV-induced depletion approaches 100% near the peak of the profile at 320 nm, indicating rapid dynamics in the B state, and corresponds to a peak absorption cross section of ∼5 × 10−17 cm2 molecule−1. The electronic spectrum for CH3CHOO is similar to that reported recently for CH2OO, but shifted 15 nm to shorter wavelength, which will result in a longer tropospheric lifetime for CH3CHOO with respect to solar photolysis. Complementary electronic structure calculations (EOM-CCSD) are carried out for the B and X potentials of these Criegee intermediates along the O–O coordinate. An intramolecular interaction stabilizes the ground state of the syn-conformer of CH3CHOO relative to anti-CH3CHOO, and indicates that the syn-conformer will be the more abundant species in the expansion. The excited B electronic state of syn-CH3CHOO is also predicted to be destabilized relative to that for anti-CH3CHOO and CH2OO, in accord with the shift in the B-X transition observed experimentally. Hydroxyl radicals produced concurrently with the generation of the Criegee intermediates are detected by 1+1′ resonance enhanced multiphoton ionization. The OH yield observed with CH3CHOO is 4-fold larger than that from CH2OO, consistent with prior studies of OH generation from alkene ozonolysis.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
Publisher:	American Institute of Physics
ISSN:	0021-9606
Last Modified:	10 Dec 2022 02:22
URI:	https://orca.cardiff.ac.uk/id/eprint/72856

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