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Kinetics of Sulfur Oxide, Sulfur Fluoride, and Sulfur Oxyfluoride Anions with Atomic Species at 298 and 500 K

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The rate constants and product-ion branching ratios for the reactions of sulfur dioxide SO2-, sulfur fluoride SF n-, and sulfur oxyfluoride anions SOxFy- with H, H2, N, N2, NO, and 0 have been measured in a selected-ion flow tube SIFT. H atoms were generated through a microwave discharge on a H2He mixture, whereas O atoms were created via N atoms titrated with NO, where the N had been created by a microwave discharge on N2. None of the ions reacted with H2, N2 or NO thus, the rate constants are 1 x 10exp 12 ccs. SOxFy- ions react with H by only fluorine-atom abstraction to form HF at 298 and 500 K. Successive F-atom removal does not occur at either temperature, and the rate constants show no temperature dependence over this limited range. SO2- and F- undergo associative detachment with H to form a neutral molecule and an electron. Theoretical calculations of the structures and energetics of HSO2 isomers were performed and showed that structural differences between the ionic and neutral HSO2 species can account for at least part of the reactivity limitations in the SO2- H reaction. All of the SOxFy- ions react with O however, only SO2- reacts with both N and O. SOxFy- reactions with N S02- excluded have a rate constant limit of 1 x 10exp 11 ccs. The rate constants for the SOxFy- reactions with H and O are 25 of the collision rate constant, as seen previously in the reactions of these ions with O3, consistent with a kinetic bottleneck limiting the reactivity. The only exceptions are the reactions of SO2- with N and O, which are much more efficient. Three pathways were observed with O atoms F-atom exchange in the reactant ion, F- exchange in the reactant ion, and charge transfer to the O atom. No associative detachment was observed in the N- and O-atom reactions.

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  • Physical Chemistry
  • Atomic and Molecular Physics and Spectroscopy

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