Absolute and relative-rate kinetics experiments and direct dynamics computations for the reaction of Br atoms with CH2ClBr

K. Imrik, Gg Kovács, I. Fejes, I. Szilágyi, D. Sarzyński, S. Dóbé, T. Bérces, F. Márta, J. Espinosa-García

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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) × 1013 exp[-(47.6 ± 0.3) kJ mol-1/RT] cm3 mol-1 s-1 (the errors given refer to la 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 thermo-chemical calculations yielding the recommended standard enthalpy of formation of ΔfHo298 (CHClBr) = (140 ± 4) kJ mol-1 (with 2σ accuracy given).

Original languageEnglish
Pages (from-to)6821-6832
Number of pages12
JournalJournal of Physical Chemistry A
Volume110
Issue number21
DOIs
Publication statusPublished - jún. 1 2006

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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