Carbon kinetic isotope effect of the reaction of CH4 with Cl atoms

The carbon kinetic isotope effect in the reaction between Cl and CH4 (KIECl) has been measured using tunable diode laser absorption spectroscopy to determine 13CH4/12CH4 ratios. Cl atoms were generated by the irradition of Cl2 in static mixtures of Cl2/CH4/N2 or Cl2/CH4/N2/O2. Both methods resulted in a (KIECl) of 1.066±0.002 at 297 K. The KIECl displayed 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 CH4 isotopic composition and may help to resolve discrepancies between measurements of stratospheric 13CH4/ 12CH4 profiles and laboratory measurements of KIEOH.