D/H kinetic isotope effect in the reaction CH₄+Cl

The D/H kinetic isotope effect (KIE Cl D ) in the reaction of CH 4 with Cl has been investigated using a tunable diode laser absorption spectrometer (TDLAS) to measure 12 CH 3 D/ 12 CH 4 ratios. A KIE Cl D of 1.508±0.041 was obtained at room temperature (296 K ). Experiments employing Fourier transform infrared measurements of 12 CH 3 D/ 12 CH 4 ratios confirmed this result. An investigation of the temperature 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 upper stratosphere, where Cl contributes substantially to the total removal of CH 4 .