CARBON KINETIC ISOTOPE EFFECT IN THE REACTION OF CH4 WITH CL ATOMS

The carbon kinetic isotope effect in the reaction between Cl and CH4 ( KIE(Cl)) has been measured using tunable diode laser absorption spectr oscopy to determine (CH4)-C-13/(CH4)-C-12 ratios. Cl atoms were genera ted by the irradition of Cl-2 in static mixtures of Cl-2/CH4/N-2 or Cl -2/CH4/N-2/O-2. Both methods resulted in a (KIE(Cl)) of 1.066 +/- 0.00 2 at 297 K. The KIE(Cl) displayed a slight temperature dependence, inc reasing to 1.075 +/- 0.005 at 223 K. This result suggests a significan t influence of the title reaction on the stratospheric CH4 isotopic co mposition and may help to resolve discrepancies between measurements o f stratospheric (CH4)-C-13/(CH4)-C-12 profiles and laboratory measurem ents of KIE(OH).