KINETICS AND MECHANISMS OF THE REACTIONS OF O-((1)D)-ATOMS WITH CF3BR AND CF2BRCF2BR IN THE GAS-PHASE AND IN SOLID ARGON MATRICES

The rate coefficients and mechanisms for the reactions of O(1D) atoms with CF3Br (halon 1301) and CF2BrCF2Br (halon 2402) have been investigated in the gas phase at room temperature. The experiments have been carried out in a static photochemical reactor. Photolysis of ozone 253.7 nm provided O(1D) atoms. The competitive reaction O(1D) + N2O has been chosen as internal standard to determine the rate coefficients. The course of the reactions was followed by FTIR spectroscopy. The measured data correspond to rate coefficients of (4.0 +/- 0.4) x 10(-11) cm3 s-1 for the reaction O(1D) + CF3Br and (8.8 +/- 1.2) x 10(-11) cm3 s-1 for the reaction O(1D) + CF2BrCF2Br. For further mechanistic studies, the reaction O(1D) + CF3Br has been investigated in solid Ar-matrices at T = 14 K. Codeposition of O3/CF3Br/Ar mixtures and irradiation at 250 nm yielded F2CO as dominant reaction product. Experiments with O-18(3) indicate that CF3OBr was formed during the course of the reaction. Our observations can be interpreted with the formation of an excited CF3OBr molecule which can be stabilized in the matrix cage or decompose rapidly to the final product F2CO. No further intermediates could be detected in the matrix experiments.