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)), CHCl2F (k(2)), and CHCIF2 (k(3)) by chlorine atoms in the ga s phase have been measured over the temperature range 298-430 K using the discharge flow/mass spectrometry technique (DF/MS) under pseudo-fi rst-order conditions with Cl atoms in large excess with respect to the halomethane. The temperature dependence of the rate coefficients is e xpressed in the Arrhenius form: k(1) = (8.0(-1.7)(+1.8)) x 10(-12) exp [-(1390 +/- 80)/T], k(2) = (5.2(-0.8)(+0.9)) x 10(-12) exp[-(1675 +/- 60)/T], k(3) = (5.3(-1.3)(+1.5)) x 10(-12) exp[-(2430 +/- 90)/T]. The units of the rate constants are cm(3) molecule(-1) s(-1) and the quote d uncertainties are 2 sigma. Wall loss and recombination of atomic chl orine (Cl + Cl + M) rate coefficients, k(w) and k(r) respectively, wer e measured and utilized in calculation of the rate coefficients. Inclu sion of the Cl atom losses is shown to be important for the slower rea ctions requiring longer reaction times. Arrhenius expressions are in g ood agreement with available literature data and in very good agreemen t with recently reported theoretical (ab initio) calculations.