A study of the reactions of trifluoromethyl sulfur pentafluoride, SF5CF3, with several positive ions of atmospheric interest

An investigation of the bimolecular reactions of several positive ions of atmospheric interest, H3O+, NO+, NO2+, O2+, H2O+, N2O+, O+, CO2+, CO+, N+ and N2+, with the greenhouse gas SF5CF3 is reported. The thermal rate coefficients and ion product distributions have been determined at 300 K using a selected ion flow tube. H3O+, NO2+ and NO+ are found to be unreactive. The reaction with O2+ proceeds with a rate coefficient significantly less than the capture value ia chemical routes, in which bonds are broken and formed. The other reagent ions, H2O+, N2O+, O+, CO2+, CO+, N+ and N2+ react with SF5CF3 with reaction rate coefficients close to or at the capture values. With the exception of the reaction with H2O+, all these efficient reactions occur by dissociative charge transfer, with CF3+ and SF3+ being the dominant product ions. CF3+ forms by direct cleavage of the S–C bond in SF5CF3+, and SF3+ probably from dissociation of (SF4+)* following intramolecular rearrangement within the lifetime of (SF5CF3+)*. For H2O+, the observed ion branching ratios suggest that the reaction proceeds ia a chemical pathway. The reactions of SF5CF3 with cations will destroy this molecule in the upper atmosphere.