14337-03-2Relevant articles and documents
Kinetics of sulfur oxide, sulfur fluoride, and sulfur oxyfluoride anions with atomic species at 298 and 500 K
Midey, Anthony J.,Viggian
, p. 1852 - 1859 (2008/10/09)
The rate constants and product-ion branching ratios for the reactions of sulfur dioxide (SO2-), sulfur fluoride (SF n-), and sulfur oxyfluoride anions (SOxF y-) with H, H2, N, N2, NO, and O have been measured in a selected-ion flow tube (SIFT). H atoms were generated through a microwave discharge on a H2/He 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 H 2, N2 or NO; thus, the rate constants are -12 cm3 s-1. 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 HSO 2 species can account for at least part of the reactivity limitations in the SO2- + H reaction. All of the SOxF y- ions react with O; however, only SO2 - reacts with both N and O. SOxFy- reactions with N (SO2- excluded) have a rate constant limit of -11 cm3 s-1. 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.
General Model for the Nonlinear pH Dynamics in the Oxidation of Sulfur(-II) Species
Rushing, C. Wayland,Thompson, Richard C.,Gao, Qingyu
, p. 11561 - 11565 (2007/10/03)
A general kinetic feature has been observed experimentally for the oxidation of the sulfur(-II) species thiosulfate, thiourea, thiocyanate, and sulfide by chlorite and other multi-equivalent oxidants under appropriate, unbuffered batch conditions. This fingerprint consists of an initial rise in pH followed by an autocatalytic drop in pH or oligo-oscillatory behavior. These systems also exhibit oscillations and other complex dynamical behavior in a continuous-flow stirred tank reactor (CSTR). The previously proposed general models that are oxidant based do not successfully explain the observed pH effects. We propose a simple, general model that is based upon the changing oxidation states of sulfur to explain the general pH features. The scheme qualitatively models autocatalysis and oligo-oscillations in batch and simple and complex oscillations in a CSTR. The general model consists of three separate stages: negative hydrogen ion feedback (S(-II) to S(0)), a transition of S(0) to S(IV), and positive proton feedback from S(IV) to S(VI).
Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. II. OCS -> S- + CO+, O- + CS+, and CO2 -> O- + CO+
Mitsuke, Koichiro,Suzuki, Shinzo,Imamura, Takashi,Koyano, Inosuke
, p. 1710 - 1719 (2007/10/02)
Ion-pair formation from photoexcitation of OCS and CO2 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 15-35 eV photon energy range.Negative ions S- and O- from OCS and O- from CO2 have been observed.The lowest onset energy in the photodissociation efficiency curve for each ion is in good agreement with the thermochemical threshold for the formation of the negative ion in the ground 2Pu state and its counterpart positive ion in the ground 2Σ+ state.There exist series of peaks with medium intensities in the efficiency curves of S- from OCS and O- from CO2; they are identified as resulting from predissociation of the Rydberg states converging to OCS+ (2Σ+) and CO2+ (2Σg+), respectively.Broad peaks are observed at 18.4 eV (ca. 675 Angstroem) in the efficiency curves for both S- and O- produced from OCS.Predissociation of the excited valence state formed by the intravalence 9? -> 10? transition is considered to mainly contribute to these features.In addition, a broadband feature is present in the wavelength range of 400-620 Angstroem in the O- efficiency curve.The most likely candidate for the corresponding doorway state is the two-electron excited state involving simultaneous 9? -> 10? and 3? -> 4? transitions.In the case of the O- efficiency curve from CO2, two maxima observed at 21.4 (580 Angstroem) and 23.0 eV (538 Angstroem) are explained as resulting from the 3?u -> 5?g transition forming an excited valence state which effectively couples to the ion-pair continuum.
Gas-Phase Nucleophilic Reactivities of Phenylnitrene (PhN-*) and Sulfur Anion Radicals (S-/.) at sp3 and Carbonyl Carbon
McDonald, Richard N.,Chowdhury, A. Kesem
, p. 198 - 207 (2007/10/02)
The reactions of PhN-/. with a series of carbonyl-containing molecules (aldehydes, ketones, and esters) were shown to proceed via an addition/fragmentation mechanism, PhN-* + R2C=O -> -)R2> -> PhN=C(O-)R + *R, producing various acyl anilide anion products.In several cases, the tetrahedral intermediate anion radicals were observed as minor ions.The intrinsic reactivity of the carbonyl-containing molecules was aldehydes > ketones > esters, where similar R groups were involved.The overall exothermicities of these reactions did not appear to play the major role in determining the relative rates (krelC=O) for these reactions.From the reaction of PhN-* with cyclobutanone, a new type of anion radical, PhN=C(O-)CH2* (m/z 133) (+ C2H4) was produced; the loss of C2H4 was considered due to the ring strain in the ketone.With cyclopentanone, cyclohexanone, and cycloheptanone, the anion radicals PhN=C(O-)(CH2)n* (n = 4-6) were the exclusive product ions.PhN-* was shown to be a poor nucleophile in SN2 displacement reactions with CH3X molecules (X = Cl, Br, O2CCF3).S-* was shown to exhibit modest SN2 nucleophilicity with CH3Cl and CH3Br.The reactions of S-* with CF3CO2R proceed via both SN2 displacement and carbonyl addition/fragmentation mechanisms: with R = CH3, the anion products were 65percent CF3CO2- and 35percent CF3COS-; from R = C2H5, the product ions were 4percent CF3CO2- and 96percent CF3COS-.These data yield the ratio kCH3/kC2H5 = 16 for SN2 displacement by S-* at these alkyl groups.The reactions of PhN-* with CO2, COS, CS2, and O2 are also reported.The reaction of PhN-* with CS2 to produce S-* as a major channel was used as the source of this atomic anion radical.In several reactions occuring at nearly the collison limit, selectivity was observed for (a) which of two reaction centers were attacked to give products and (b) which of two mechanisms would be dominant in the overall reaction.
Negative ion-molecule reactions of SF4
Babcock, Lucia M.,Streit, Gerald E.
, p. 3864 - 3870 (2007/10/02)
A study of some negative ion-molecule reactions involving SF4 has been carried ot by the flowing afterglow technique at ambient temperature.By ezamining a series of charge exchange reactions of SF4 and SF4-, the electron affinity of SF4 has been determined to be 2.35+/-0.1 eV.Rate coefficients for the charge exchange reactions of HS-, S-, OH-, and O- with SF4 and of SF4- with Cl2 and NO2 are reported.In addition, the fluoride transfer reactions of SF4- and SF6- with SF4 to produce SF5- have been examined.That both reactions proceed indicates that the fluoride affinity of SF4 is greater than that of SF3 or SF5.A lower limit of 3.7 eV for the electron affinity of SF5 may also be deduced from the fluoride transfer reactions.The two body addition of halide ions (X-) to SF4 to form the adduct SF4X- proceeds at near the collision limit (k=9.7*10-10cm3molecule-1s-1) for F-, very slowly (k=2.6*10-11cm3molecule-1s-1) for Cl-1, and not at all within experimental limits (k-12cm3molecule-1s-1) for Br-1.
