UV absorption spectra of methyl-substituted hydroxy-cyclohexadienyl radicals in the gas phase

Document Type

Article

Publication Date

12-14-2005

Abstract

UV absorption spectra of five methyl-substituted hydroxy-cyclohexadienyl radicals, formed by the addition of the hydroxyl radical (OH) to toluene (methyl benzene), o-, m- and p-xylene (1,2-, 1,3- and 1,4-dimethyl benzene, respectively) and mesitylene (1,3,5-trimethylbenzene), have been determined at 298 K, 1 atm pressure (N2 + O2), and the corresponding absolute absorption cross-sections measured, using laser flash photolysis and time-resolved UV absorption detection. As observed for other cyclohexadienyl-type radicals, a strong absorption band is present in the 260-340 nm spectral region, with maximum cross-sections in the range (0.9-2.2) × 10-17 cm2 molecule-1. The shape of the band varies significantly from one radical to the next for the series of aromatic precursors investigated. The nature and yields of hydroxylated ring-retaining oxidation products, identified in previous studies of the OH-initiated oxidation of aromatic hydrocarbons, and the results of theoretical density functional theory (DFT) calculations indicate that one or more possible isomers of the various OH-adducts may contribute to the observed spectra. Isomers where the OH-group is ortho- (or both ortho- and ipso-) to a substituent methyl-group are likely to be the most abundant but other isomers may also be formed to a significant extent. Nonetheless, the present study provides absorption spectra of the adduct radicals formed from the gas phase addition of OH to the aromatic hydrocarbons considered, near room temperature and 1 atm pressure. © 2005 Elsevier B.V. All rights reserved.

Identifier

28444464079 (Scopus)

Publication Title

Journal of Photochemistry and Photobiology A Chemistry

External Full Text Location

https://doi.org/10.1016/j.jphotochem.2005.09.016

ISSN

10106030

First Page

98

Last Page

106

Issue

1-3 SPEC. ISS.

Volume

176

Grant

EVK2-CT-1999-00053

Fund Ref

European Commission

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