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 CH 4 with Cl at temperatures between 273 and 350 K. Isotope ratio mass spectrometry was utilized to measure 13 CH 4 / 12 CH 4 and CH 3 D/CH 4 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.