Kinetic isotope effects in the gas phase reactions of OH and Cl with CH₃Cl, CD₃Cl, and ¹³CH₃Cl

Abstract. The kinetic isotope effects in the reactions of CH₃Cl, ¹³CH₃Cl and CD₃Cl with OH radicals and Cl atoms were studied in relative rate experiments at 298±2 K and 1013±10 mbar. The reactions were carried out in a smog chamber using long path FTIR detection and the spectroscopic data analyzed employing a non-linear least squares spectral fitting method using measured high-resolution infrared spectra as well as absorption cross sections from the HITRAN database. The reaction rates of ¹³CH₃Cl and CD₃Cl with OH and Cl were determined relative to CH₃Cl as: k_OH+CH3Clk_OH+CH3Cl/k_OH+13CH3Cl}k_OH+13CH3Cl=1.059±0.008, k_OH+CH3Clk_OH+CH3Cl/k_OH+CD3Clk_OH+CD3Cl=3.9±0.4, k_Cl+CH3Clk_Cl+CH3Cl/k_Cl+13CH3Clk_Cl+13CH3Cl =1.070±0.010 and k_Cl+CH3Clk_Cl+CH3Cl/k_Cl+CD3Clk_Cl+CD3Cl=4.91±0.07. The uncertainties given are 2σ from the statistical analyses and do not include possible systematic errors. The unexpectedly large ¹³C kinetic isotope effect in the OH reaction of CH₃Cl has important implications for the global emission inventory of CH₃Cl.