Experimentally determined kinetic isotope effects in the reaction of CH4 with Cl: Implications for atmospheric CH4

Abstract

We report experimental values for the carbon and hydrogen kinetic isotope effects (KIEs) in the reaction of CH4 with Cl at temperatures between 273 and 350 K. Isotope ratio mass spectrometry was utilized to measure 13CH4/12CH4 and CH3D/CH4 ratios on samples taken from a 5870- L reaction chamber. At 299 K, k(c12)/k(c13) = 1.0621±0.0001 (2σ) and k(h)/k(d) = 1.474±0.020 (2σ). For both KIEs, the ratio decreased with increasing temperature over the range studied. These results agree well with experimental studies using tunable diode laser absorption spectroscopy and FTIR absorption spectroscopy and with a recent theoretically-calculated set of values.