Investigation of gas phase reactions of OH radicals with fluoromethane and difluoromethane using Ar-sensitized pulse radiolysis

Hydroxyl radical reactions were studied in gas phase CH3F and CH2F2 systems using an Ar-sensitized pulse radiolysis-absorption spectroscopy technique. Bimolecular H-atom abstraction rate constants were determined empirically by fitting the observed OH decay data to a first-order law, then plotting the apparent first-order rate constants against substrate concentration. The resulting values of the bimolecular rate constants in cm3molec-1 s-1 are (1.71 ± 0.24) x 10-14 for OH + CH3F and (0.88 ± 0.14) x 10-14 for OH + CH2F2. Both values are in good agreement with previous results. Kinetic modeling showed a substantial contribution of radical-radical reactions to OH loss in both cases, but the data reduction procedure was successful in distinguishing the contribution due to the bimolecular OH-substrate abstraction process. Observed and computer simulated OH decay curves match satisfactorily for typical experiments, using initial OH concentrations and OH abstraction rate constants which were within ± 10% of the measured values. (author)