The carbon kinetic isotope effect in the reaction between Cl and CH4(KIECl) has been measured using tunable diode laser absorption spectroscopy to determine13CH4/12CH4ratios. Cl atoms were generated by the irradition of Cl2in static mixtures of Cl2/CH4/N2or Cl2/CH4/N2/O2. Both methods resulted in a (KIECl) of 1.066±0.002 at 297 K. The KIECldisplayed a slight temperature dependence, increasing to 1.075±0.005 at 223 K. This result suggests a significant influence of the title reaction on the stratospheric CH4isotopic composition and may help to resolve discrepancies between measurements of stratospheric13CH4/12CH4profiles and laboratory measurements of KIEO
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