RATE COEFFICIENTS OF THE REACTIONS OF CHLORINE ATOMS WITH HALOETHANESOF TYPE CH3CCL3-XFX (X=0, 1, AND 2) - EXPERIMENTAL AND AB-INITIO THEORETICAL-STUDIES

The absolute rate coefficients for the hydrogen abstraction reactions from CH3CCl3(k(1)), CH3CCl2F (k(2)), and CH3CClF2 (k(3)) by chlorine a toms in gas phase have been measured as a function of temperature usin g the discharge flow/mass spectrometric technique (DF/MS). The reactio ns were investigated under pseudo-first-order conditions with Cl atoms in large excess with respect to the haloethanes. The temperature depe ndence of the rate coefficients is expressed in the Arrhenius form: k( 1)(298-416K) = (2.8-(4.1)(1.7+)) x 10(-12) exp[-(1790 +/- 320)/T], k(2 )(299-429K) = (3.0(-1.3)(+2.4)) x 10(-12) exp[-(2220 +/- 150)/T], k(3) (298-438K) = (1.5(-1.0)(+3.1)) x 10(-12) exp[-(2420 +/- 400)/T]. The u nits of the rate constants are cm(3) molecule(-1) s(-1), and the quote d uncertainties are +/-2 sigma. For understanding the reaction path me chanism of the chlorination of the studied halogen-substituted ethanes , ab initio molecular orbital calculations were performed. Transition state structures were determined. These calculations lead to predictio ns of preexponential factors in the same order of magnitude of measure d values, The ab initio energetics of the reactions were corrected usi ng the ISO-M method, a mixing of isodesmic reactions for obtaining rea ction enthalpies and concept of intrinsic energy of Marcus to deduce a ctivation energies. A reasonably good agreement with the experimental values were found.