Temperature Dependence of Rate Coefficients for the Reactions of Chlorine Atoms with Halomethanes of Type CHCl_3-xF_x (x = 0, 1, and 2)

Abstract

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: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.

Thermochemistry data from kinetics results: A test of quality of the potential energy surface

“…2 together with experimental values for comparison. The theoretical values agree with the experiments [15] and a recent review [16] in the common temperature range, 296-410 K. In general, this agreement lends confidence to the surfaces constructed for these reactions, However, discrepancies still remain that can be analyzed using the test proposed in this Letter. The phenomenological forward and reverse activation energies at 298 K for the three reactions are listed in Table 2, together with the standard reaction enthalpies.…”

Environmental effects of large igneous province magmatism: a Siberian perspective

“…The relative rate study of Knox [730] yields a similiar temperature dependence to that recommended but with rate constant values systematically lower than other studies. The absolute study by Talhaoui et al [1278] yielded a 298 K rate constant somewhat lower than recommended and a temperature dependence somewhat higher. For this evaluation all of the relative rate measurements were recalculated based on the current recommendations for the rate constant of the reference reactions.…”

“…Cl + CHFCl 2 (HCFC-21). The recommended value for k(298 K) is the average of the results from the relative rate study of Tuazon et al [1326] and the absolute rate study of Talhaoui et al [1278]. These results are preferred over the earlier room temperature results of Glavas and Heicklen [508].…”

“…Cl + CHF 2 Cl (HCFC-22). The recommended value for k(298 K) is the mean of the values derived in the relative rate study by Tuazon et al [1326] and in the absolute rate studies of Jourdain et al [682] and Talhaoui et al [1278] (which is assumed to supercede the earlier study by Sawerysyn et al [1151]). The temperature dependence is from Talhaoui et al The A-factor from that study has been adjusted to fit the recommended room temperature value.…”

Isodesmic Reactions for Transition States: Reactions of Cl Atoms with Methane and Halogenated Methanes

“…These reactions are presented in Table 1 along with the sources of this information. 10,[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] For some of the reactions, several sources of rate constant values are available. In such cases, preference is given to data obtained in direct experiments.…”