Gas phase reactions of SF6, SF5Cl, and SF5CF3 with bare iron ions, FeX+ (5Δ) (X= F, Cl, Br, I), and FeO+ (6Σ) were carried out in a selected ion drift cell apparatus operated at room temperature and a total pressure of 3.5 torr of helium. Rate coefficients and product branching fraction data were obtained for all reactions in order to evaluate reaction efficiencies and possible mechanisms. For SF6 reactions with ligated iron ions, single and double association products were observed in all cases. Dependent on the ligand, various fluoride abstractions were also observed in small amounts, except with FeF+ where SF5+ was a much larger contributor to the product formation. For SF6 reactions with bare iron ions only fluoride abstractions were observed in agreement with previous studies. In the reactions involving SF5Cl, various bimolecular products including SF2+, SF3+, SF4+, and SF5+ were seen dependent on the reactant ion. Association was not observed with this neutral reactant. SF3+ typically dominated product formation with SF5Cl. SF5CF3 likewise exhibited various product channels dependent on the ligand. For reactions with Fe+ and FeO+, products include SFx+ (x=1-3) and CF3+. In reactions of FeO+ with SF5CF3 oxygen transfer produced SOF+. Both Fe+ and FeO+ reactions with SF5CF3 were found to be highly efficient. A ligand effect was observed in the efficiencies of reactions with SF6 which generally correlates with the electronegativity of the substituent on the iron center. This ligand effect is not observed with SF5Cl, suggesting that the strength of the activated bond is involved in the rate determining step for these two neutral substrates. In cases in which experimental thermochemistry was unavailable, reaction energetics were determined computationally using density functional methods. In cases in which comparisons were possible, calculated reaction thermochemistry was generally in agreement experimental values.

Tuning efficiency and product formation in the iron-Induced decomposition of the potent greenhouse gas SF6 and its analogs SF5Cl and SF5CF3

2019 Spring National Meeting

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