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

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