Positive ion chemistry related to hydrocarbon flames doped with CF3 Br

Reactions of positive ions known to be present in hydrocarbon flames have been studied for their reactivity toward the fire suppressant CF3Br (Halon 1301) at 300 and 525 K. Rate constants and product branching percentages were measured at the two temperatures. The ions HCO+, CH+3, and CH+5 reacted rapidly with CF3Br producing CF+3 and CF2Br+ in all three cases. For CH+5, proton transfer was also observed at 300K. The ions H2COH+, H3COH+2, and H3O+ were unreactive with CF3Br at 300 and 525 K, and at ≈0.5 eV of collision energy supplied by a drift tube at 300 K. The product ions CF+3 and CF2Br+ were studied in separate experiments for reactivity toward selected hydrocarbons, and rate constants and branching percentages were determined. The hydrocarbons CH4, C2H6, C3H8, C2 H4, C3 H6, and C2H2 were selected for study (CF2] Br+ was studied with CH4, C2 H6, C2 H4, and C2H2 only). Neither CF+3 nor CF2Br+ reacted with CH4, but both ions reacted with other hydrocarbons. Hydrogen fluoride was among the inferred neutral reaction products in the reactions of CF+3 with C2H4 and C3H6. We found no evidence for any ionic process which could release Br atoms, any other free radicals, or the CF3Br+ molecular ion, and therefore no evidence was found to indicate that ions play a role in flame inhibition by CF3Br.