title: Absolute and relative-rate kinetics experiments and direct dynamics computations for the reaction of Br atoms with CH2ClBr.
abstract: Kinetics of the reaction Br + CH2ClBr <--> CHClBr + HBr (1, -1) were studied experimentally in the forward direction. The absolute reaction kinetics method of laser flash photolysis coupled with Br atom resonance fluorescence detection and three different relative-rate methods with gas-chromatographic analysis were applied to carry out the experiments. The rate constants determined were found to obey the Arrhenius law in the wide temperature range of T = 293-785 K providing the kinetic expression k1 = (2.8 +/- 0.1) x 10(13) exp[-(47.6 +/- 0.3) kJ mol(-1)/RT] cm3 mol(-1) s(-1) (the errors given refer to 1sigma precision). An ab initio direct dynamics method was used to study reaction (1, -1) theoretically. The electronic structure information including geometries, gradients, and force constants was obtained at the MP2 level of theory; and energies were improved at higher theoretical levels. Rate constants were calculated using the canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-1000 K. Theory substantially underestimates k1 compared to experiment. The agreement was found good with k(-1) reported previously predicting positive temperature dependence. The experimental kinetic parameters were utilized in thermochemical calculations yielding the recommended standard enthalpy of formation of delta(f)H degrees (298) (CHClBr) = (140 +/- 4) kJ mol(-1) (with 2sigma accuracy given).
authors.affiliation: Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59-67, Budapest H-1025, Hungary.
authors.forename: K
authors.initials: K
authors.lastname: Imrik
authors.forename: Gg
authors.initials: G
authors.lastname: Kovacs
authors.forename: I
authors.initials: I
authors.lastname: Fejes
authors.forename: I
authors.initials: I
authors.lastname: Szilagyi
authors.forename: D
authors.initials: D
authors.lastname: Sarzyński
authors.forename: S
authors.initials: S
authors.lastname: Dóbé
authors.forename: T
authors.initials: T
authors.lastname: Bérces
authors.forename: F
authors.initials: F
authors.lastname: Marta
authors.forename: J
authors.initials: J
authors.lastname: Espinosa-García