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

Abstract

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.