Carbon kinetic isotope effect in the reaction CH4+Cl: a relative rate study using FTIR spectroscopy

The 12C/13C kinetic isotope effect in the reaction of methane with chlorine atoms (KIECl12C/13C) was investigated at 298 K using photolysis of static Cl2/CH4/N2 mixtures, with in-situ analysis of isotopic composition by FTIR absorption spectroscopy. Least squares fitting of composite 12CH4/13CH4 spectra to reference spectra obtained at the same temperature, pressure and resolution enabled the relative 12CH4:13CH4 content to be measured at a high precision. The result obtained was KIECl12C/13C(298 K)=1.066±0.002 (2σ), in excellent agreement with the single previous experimental determination at this temperature. This result confirms the unexpectedly high fractionation in the title reaction.