Temperature Dependence of Rate Coefficients for the Reactions of Chlorine Atoms with Halomethanes of Type CHCl₃₋xFx (x = 0, 1, and 2)

The rate coefficients for the hydrogen abstraction reactions from CHCl 3 ( k 1 ), CHCl 2 F ( k 2 ), and CHClF 2 ( k 3 ) by chlorine atoms in the gas phase have been measured over the temperature range 298−430 K using the discharge flow/mass spectrometry technique (DF/MS) under pseudo-first-order conditions with Cl atoms in large excess with respect to the halomethane. The temperature dependence of the rate coefficients is expressed in the Arrhenius form: k 1 = ( ) × 10 -12 exp[−(1390 ± 80)/ T ], k 2 = ( ) × 10 -12 exp[−(1675 ± 60)/ T ], k 3 = ( ) × 10 -12 exp[−(2430 ± 90)/ T ]. The units of the rate constants are cm 3 molecule -1 s -1 and the quoted uncertainties are 2σ. Wall loss and recombination of atomic chlorine (Cl + Cl + M) rate coefficients, k w and k r respectively, were measured and utilized in calculation of the rate coefficients. Inclusion of the Cl atom losses is shown to be important for the slower reactions requiring longer reaction times. Arrhenius expressions are in good agreement with available literature data and in very good agreement with recently reported theoretical (ab initio) calculations.