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).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry