Gas-Phase Chemistry and Thermochemistry of the Hydroxysulfide Anion, HOS(1-)

Article abstract of DOI:10.1021/j100132a026

The chemistry and thermochemistry of the hydroxysulfide anion, HOS(1-), has been studied in a tandem flowing afterglow-selected ion flow tube (FA-SIFT).The reactions of HOS(1-) with O2, CO, CO2, CS2, SO2, H2S, (CH3)3CSH, CH3SH, CH3Cl, and (CH3)2CHCl have been examined and compared to the corresponding reactions of HOO(1-).The gas-phase basicity of HOS(1-) has been established via the bracketing technique <ΔG⁰_acid(HOSH) = 347 +/- 3 kcal mol^-1, ΔH⁰_acid(HOSH) = 354 +/- 3.5 kcal mol^-1>.Ab initio calculations have been carried out on HOS(1-), HSO(1-), HOSH, and H2SO which demonstrate that HOS(1-) and HOSH are the more stable isomers.At the MP4SDTQ(FC)/6-311++G**//MP2(Full)/6-311++G** level of theory, these calculations predict ΔH⁰_acid(HOSH) = 356.7 kcal mol^-1, in agreement with the experimentally determined value.Measurement of the forward and reverse rate constants for the reaction generating HOS(1-) yields ΔH⁰_f(HOS(1-)) = -38.7 +/- 2 kcal mol^-1, which when combined with the experimental electron affinity of HOS, determines ΔH⁰_f(HOS) = -0.5 +/- 2 kcal mol^-1; this value is in good agreement with a recent ab initio determination.The gas-phase basicity of HSS(1-), the major product ion in the reaction of HOS(1-) and CS2, has also been determined via the bracketing technique <ΔG⁰_acid(HSSH) = 339 +/- 3 kcal mol^-1, ΔH⁰_acid(HSSH) = 346 +/- 3.5 kcal mol^-1>.Combination of our gas-phase acidity values for HOSH and HSSH as well as for CH3SSH reported in a previous paper, with known electron affinities for the corresponding radicals, allows determination of the S-H bond dissociation energies (D₂₉₈): HOSH (79 +/- 3.5 kcal mol^-1), HSSH (76 +/- 3.5 kcal mol^-1), and CH3SSH (79 +/- 3.5 kcal mol^-1).