Kinetics of the combination reactions of chlorofluoromethylperoxy radicals with NO2in the temperature range 233–373 K

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Abstract
The rate parameters for the combination reactions of CCl3O2, CCl2FO2 and CF3O2 radicals with NO2 were measured in the pressure range 1–10 Torr and from 233 to 373 K. Experiments were performed by pulsed laser photolysis and time-resolved mass spectrometry. Al reactions are in the fall-off region and are significantly faster than the equivalent reaction of CH3O2. They exhibit strong negative temperature coefficients and the rate constants increase in the series from CF3O2 to CCl3O2. The experimental equilibrium constant was obtained for the reaction of CCl2FO2 at 273 K, by using previously determined rate constants for the reverse reaction. This determination allowed us to obtain ΔH° of the reaction by calculating the structural and spectroscopic parameters by the semi-empirical MNDO method. Assuming that the value of ΔH° is the same for all reactions of the series it was possible to calculate the temperature dependence of all equilibrium constants and the bond dissociation energies D° 298(CX3O2—NO2)= 105 ± 5 kJ mol–1(X = For Cl). ARRKM model was set up for these reactions and calibrated for the reaction of CCl2FO2. The model is shown to reproduce quite adequately the fall-off curves and with the substitution of chlorine for fluorine in the series of radicals investigated. This model was used to extrapolate the low-pressure data to high pressure, where no experimental data were available, and to calculate the kinetic parameters for the CClF2O2 reaction, which could not be investigated experimentally in the present study. Kinetic parameters are reported for the association reaction of the entire series of chlorofluoromethylperoxy radicals with NO2.

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