A study of the reactions of trifluoromethyl sulphur 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.