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

Abstract

The carbon kinetic isotope effect in the reaction between Cl and CH 4 (KIE Cl ) has been measured using tunable diode laser absorption spectroscopy to determine 13 CH 4 / 12 CH 4 ratios. Cl atoms were generated by the irradition of Cl 2 in static mixtures of Cl 2 /CH 4 /N 2 or Cl 2 /CH 4 /N 2 /O 2 . Both methods resulted in a (KIE Cl ) of 1.066±0.002 at 297 K. The KIE Cl 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 CH 4 isotopic composition and may help to resolve discrepancies between measurements of stratospheric 13 CH 4/ 12 CH 4 profiles and laboratory measurements of KIE OH.