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

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.