Carbon kinetic isotope effects in the gas-phase reactions of aromatic hydrocarbons wih the OH radical at 296 ± 4 K

Abstract

The carbon kinetic isotope effects (KIEs) of the room temperature reactions of benzene and several light alkyl benzenes with OH radicals were studied in a reaction chamber at ambient pressure using gas chromatography coupled with online combustion and isotope ratio mass spectrometry (GCC-IRMS). The KIEs are reported in per mil according to ε (‰) = (KIE - 1) × 1000, where KIE = k12 /k13. The following average KIEs were obtained, (all in ‰): benzene 7.53 ± 0.50; toluene 5.95 ± 0.28; ethylbenzene 4.34 ± 0.28; o-xylene 4.27 ± 0.05, p-xylene 4.83 ± 0.81; o-ethyltoluene 4.71 ± 0.12 and 1,2,4-trimethylbenzene 3.18 ± 0.09. Our KIE value for benzene + OH agrees with the only reported value known to us [Rudolph et al., 2000]. It is shown that measurements of the stable carbon isotope ratios of light aromatic compounds should be extremely useful to study atmospheric processing by the OH radical. Copyright 2004 by the American Geophysical Union.