D H KINETIC ISOTOPE EFFECT IN THE REACTION CH4+CL/

The D/H kinetic isotope effect (KIE(Cl)(D)) in the reaction of CH4 wit h Cl has been investigated using a tunable diode laser absorption spec trometer (TDLAS) to measure (CH3D)-C-12/(CH4)-C-12 ratios. A KIE(Cl)(D ) of 1.508 +/- 0.041 was obtained at room temperature (296 K). Experim ents employing Fourier transform infrared measurements of (CH3D)-C-12/ (CH4)-C-12 ratios confirmed this result. An investigation of the tempe rature dependence showed an increase of KIE(Cl)(D) (1.592 +/- 0.057 at 223 K) with decreasing temperature. This very large D/H fractionation effect affects the overall isotope fractionation in the middle and up per stratosphere, where Cl contributes substantially to the total remo val of CH4.