The Hydrogen Kinetic Isotope Effects of the Reactions of <Emphasis Type="Italic">n</Emphasis>-Alkanes with Chlorine Atoms in the Gas Phase |
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| Authors: | R?Iannone R?S?Anderson A?Vogel P?S?Eby M?J?Whiticar Email author" target="_blank">J?RudolphEmail author |
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| Institution: | 1.Institut für Chemie und Dynamik der Geosph?re,ICG-II: Troposph?re,Forschungszentrum Jülich,Germany;2.Centre for Atmospheric Chemistry,York University,Toronto,Canada;3.Biogeochemistry Facility, School of Earth and Ocean Sciences,University of Victoria,Victoria,Canada |
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| Abstract: | The stable-hydrogen kinetic isotope effects (KIEs) for a series of n-alkanes in reaction with chlorine atoms in the gas phase were studied in a 25-L PTFE reaction chamber at 298 K. The time
dependence of both the stable hydrogen isotope ratios and the concentrations was determined using a gas chromatography pyrolysis
isotope ratio mass spectrometry (GC-P-IRMS) system. The following KIE values, in per mil (‰), were obtained: 39.6 ± 2.7 (n-butane), 28.2 ± 0.9 (n-pentane), 24.6 ± 1.0 (n-hexane), 24.0 ± 1.2 (n-heptane), 17.9 ± 3.3 (n-octane), 15.1 ± 0.7 (n-nonane), and 14.9 ± 1.8 (n-decane). The errors given are the ±1σ standard errors. These measured values were used to derive structure–reactivity relationship
(SRRs), which allow for the calculation of the KIEs for the reaction of n-alkanes with Cl atoms. The results of the calculations agree with the measurements within few per mil or better. The site
specific stable hydrogen isotope fractionation effects for methyl groups are approximately a factor of 3 larger than those
for methylene group, a finding which is qualitatively similar to site-specific stable hydrogen isotope effects reported in
literature for reactions of alkanes with the OH radical. Because n-alkanes with close to natural isotope ratios (i.e. neither artificially labeled, nor enriched or depleted) were used, the
KIE data are directly applicable to atmospheric studies. Based on these KIE values, the impact of Cl-atom reactions of the
stable hydrogen isotope ratio on alkanes are estimated for different levels of Cl-atom concentrations. On average in the troposphere,
the impact of Cl-atom reactions of the stable hydrogen isotope ratio of n-alkanes will be small. However, in regions of the troposphere with high concentrations of Cl atoms, such as the tropospheric
ozone depletion episodes during polar sunrise, the impact of Cl-atom reactions is substantial.
An erratum to this article is available at . |
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| Keywords: | stable isotope ratios kinetic isotope effects non-methane hydrocarbons deuterium tropospheric Cl atoms |
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