- TEA CO 2 laser-induced isotopically selective dissociation of SF 6 in a cold shock wave
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When a pulsed gas dynamically cooled supersonic molecular flow interacts with solid surface a cold shock wave is formed in front of it, non-equilibrium conditions in which may be 'reverse' to those in the incident (unperturbed) flow. Isotopically selective infrared multiphoton dissociation of SF6 in the cold shock wave was studied. Anomalously a large increase (more than one order of magnitude) of the yield of products was found, as compared with the case of excitation of SF6 in unperturbed flow, without essential decrease of the selectivity of process.
- Makarov,Petin
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- Pentafluoronitrosulfane, SF5NO2
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The synthesis of pentafluoronitrosulfane, SF5NO2, is accomplished either by reacting N(SF5)3 with NO 2 or by the photolysis of a SF5Br/NO2 mixture using diazo lamps. The product is purified by treatment with CsF and repeated trap-to-trap condensation. The solid compound melts at -78°C, and the extrapolated boiling point is 9°C. SF5NO2 is characterized by 19F, 15N NMR, IR, Raman, and UV spectroscopy as well as by mass spectrometry. The molecular structure of SF 5NO2 is determined by gas electron diffraction. The molecule possesses C2v symmetry with the NO2 group staggering the equatorial S-F bonds and an extremely long 1.903(7) A S-N bond. Calculated bond enthalpies depend strongly on the computational method: 159 (MP2/6-311G++(3df)) and 87 kJ mol-1 (B3LYP/6-311++G-(3df)). The experimental geometry and vibrational spectrum are reproduced reasonably well by quantum chemical calculations.
- Lu, Norman,Thrasher, Joseph S.,Von Ahsen, Stefan,Willner, Helge,Hnyk, Drahomir,Oberhammer, Heinz
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p. 1783 - 1788
(2008/10/09)
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- Quantitative infrared spectroscopic analysis of SF6 decomposition products obtained by electrical partial discharges and sparks using PLS-calibrations
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Infrared spectroscopy is a powerful tool for the analysis of gaseous by-products in sulfur hexafluoride gas used as an insulator in high-voltage equipment. Sparks and electrical partial discharges were generated between different point-plane configurations within a custom-made discharge chamber constructed from stainless steel and Teflon. Various electrode materials were used such as stainless steel, copper, aluminium, silver, tungsten and tungsten/copper alloy. Owing to the different electrical conditions, a wide concentration range of the decomposition products existed. The main-products found were the sulfuroxyfluorides SOF4 and SOF2, as well as HF following experiments with partial discharges and sparking with energies around 1.0 J/spark. All infrared spectra were recorded using an FTIR-spectrometer equipped with a 10 cm gas cell. Quantification was carried out using classical least-squares and partial least-squares (PLS) with multivariate spectral data from selected intervals. PLS calibration models were also optimised under the constraint of a minimum number of spectral variables with a view to developing simple photometers based on a restricted number of laser wavelengths. Standard errors of prediction obtained by cross-validation of different PLS calibration models are reported for the compounds mentioned, as well as for SF4, SO2F2 and SiF4.
- Kurte,Heise,Klockow
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p. 505 - 513
(2007/10/03)
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- Spectrum and Mutual Kinetics of HOCH2CH2O2 Radicals
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β-Hydroxyethyl peroxy radicals have been studied by using pulse radiolysis to generate the radicals and kinetic absorption to monitor their formation and decay.The ultraviolet absorption spectrum assigned to HOCH2CH2O2 is broadband in nature with a maximum absorption cross section of 3.5 (+/-0.6) * 10-18 cm2 molecule-1 at 230 nm.An overall rate constant for the self-reaction 2 HOCH2CH2O2 -> HOCH2CH2OH + HOCH2CHO + O2 (3a), 2 HOCH2CH2O2 -> 2 HOCH2CH2O + O2 (3b) of k3 = 7.7 (+/-1.2) * 10-12 cm3 molecule-1 s-1 was measured at room temperature together with an estimation of the branching ratio, k3a/k3 = 0.75 (+/-0.1).
- Anastasi, C.,Muir, D. J.,Simpson V. J.
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p. 5791 - 5797
(2007/10/02)
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- Gas-Phase Lewis Acid-Base Interactions. An Experimental Determination of Cyanide Binding Energies from Ion Cyclotron Resonance and High-Pressure Mass Spectrometric Equilibrium Measurements
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Both ion cyclotron resonance and high-pressure mass spectrometric equilibrium techniques have been used to investigate the binding energies of anions to a variety of Lewis acids.From an analysis of the enthalpy changes associated with CN- binding it is evident that in cases of relatively weak binding considerable freedom of rotational motion of CN- in the complex may be retained.Ab initio calculations and experiment suggest that binding through both the N and C sites of CN- is nearly equally favorable in some cases.In contrast to results previously obtained for Bronsted acids which showed that CN- and Cl- bind nearly identically, the present data for Lewis acids show many cases where cyanide is much more favorably bound than chloride, a consequence of enhanced covalent binding of the CN- complexes.New Kroeger Drago parameters derived for CN- support the importance of covalent binding in cyanide adducts.Correlations of binding energy of anions to Lewis acids with the anion proton affinity show excellent linear relationships which may be used to predict binding energetics for new anions.
- Larson, J. W.,Szulejko, J. E.,McMahon, T. B.
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p. 7604 - 7609
(2007/10/02)
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- Preparation and characterization of chlorodifluorosulfur(IV) hexafluoroarsenate
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The stable salt [SF2Cl]+[AsF6]- was prepared and isolated in good yield from the reaction of trans-CF3SF4Cl and AsF5. The identity and ionic nature of this salt were established by its elemental analysis and by 19F NMR, IR, and mass spectral studies. Redistribution of the halogen atoms in the cation of [SF2Cl]+[AsF6]- to form [SF3]+[AsF6]- and [SCl3]+[AsF6]- in liquid SO2 occurred at ambient temperature. In the presence of NaF or NaCl, [SF2Cl]+ was converted to [SF3Cl] or [SF2Cl2], respectively, at low temperature, where redistribution occurred to form SF4 and [SCl4].
- Alam, Kohrshed,Shreeve, Jean'ne M.
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p. 1374 - 1375
(2008/10/08)
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- Attempted Synthesis of Osmium(VI) and Iridium(VI) Thiofluorides; the Preparation of OsF5.SF4 and IrF5.SF4
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The interaction of OsF4 or IrF4 with ZnS or B2S3 at elevated temperature yields the adducts OsF5.SF4 and IrF5.SF4 rather than the trasition-metal thiofluorides.Infrared and X-ray powder diffraction studies indicate that the adducts have contributions to the bonding from the ionic formulations +- and +- and there is also (19)F n.m.r. evidence for the latter in solution in anhydrous HF.
- Holloway, John. H,Rook, John
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p. 2285 - 2288
(2007/10/02)
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- Ion Chemistry and Electron Affinity of WF6
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The rate coefficients and branching ratios have been measured for the reactions of WF6 with F(-),Cl(1-), Br(1-), I(1-),CN(1-),NO3(1-), NO2(1-),SF5(1-) and SF6(1-).WF6 was found to react rapidly with these ions.Three channels were observed: asociation, cha
- Viggiano, A. A.,Paulson, John, F.,Dale, Fred,Henchman, Michael,Adams,N. G.,Smith, D.
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p. 2264 - 2267
(2007/10/02)
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- INTERACTION BETWEEN URANIUM PENTAFLUORIDE AND THE PENTAFLUORIDES OF VANADIUM, ARSENIC, NIOBIUM, TANTALUM, AND BISMUTH, AND THE TETRAFLUORIDE OF SULPHUR
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The interaction of UF5 with SF4, SF4O, and some Lewis-acid pentafluorides of various strengths has been studied.In anhydrous HF solutions, SF4 was shown to yield an adduct of composition 3UF5*SF4 in which both ionic and fluorine-bridged species are present.The pentafluorides of arsenic, tantalum, and niobium combine with UF5 to give adducts of composition 1.5 UF5*AsF5, UF5*2TaF5, and UF5*2NbF5, respectively.The arsenic derivative is stable at room temperature only under a pressure of AsF5, whereas the tantalum and niobium adducts decompose at higher temperature forming UF5*TaF5 and UF5*NbF5, respectively.Vibrational spectroscopic study of the pentafluoride adducts of UF5 has shown that they consist of covalent fluorine-bridged species.Uranium pentafluoride is fluorinated at room temperature by VF5 and by BiF5 in anhydrous HF.
- Holloway, John H.,Staunton, Garry M.,Rediess, Klaus,Bougon, Roland,Brown, David
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p. 2163 - 2166
(2007/10/02)
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- The Reaction of S2NAsF6 with Halogens: Preparation and X-Ray Crystal Structure of Bis(difluorothio)nitronium Hexafluoroarsenate(V), (SF2)2NAsF6; Preparation of (SBr)2NAsF6, and Vibrational Spectrum and Normal-co-ordinate Analysis of the (SX)2N+ (X=Cl or Br) Cations
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Solutions of S2NAsF6 in liquid SO2 react with elemental chlorine and bromine yielding (SX)2NAsF6 (X=Cl or Br), essentially quantitatively.No reaction was detected with iodine.The vibrational spectrum of (SBr)2N+ was similar to that of (SCl)2N+ of known structure, implying a similar structure for the bromine derivative.This conclusion was supported by a normal-co-ordinate analysis of (SX)2N+.The analysis was consistent with some positive interaction between the halogen atoms in (SX)2N+, possibly accounting for the cis planar geometry of these cations.Attempts to prepare (SF)2NAsF6 were unsuccessful.However, (SF2)2NAsF6 was synthesised by the reaction of S2NAsF6 and XeF2 in liquid SO2F2, essentially quantitatively.The structure of (SF2)2NAsF6 was determined by X-ray diffraction.The crystals are orthorhombic with a=14.909(1), b=9.843(4), c=12.113(1) Angstroem, and Z=8.The structure was refined in space group Pbca to a conventional R factor of 0.076 for 902 independent reflections with I>2?(I).It consists of discrete (SF2)2N+ and AsF6- with some cation-anion interactions.The (SF2)2N+ cation has approximate C2γ symmetry with essentially eclipsed fluorine-sulphur bonds as viewed along the sulphur-sulphur axis.The average S-N and S-F distances are 1.551(10) and 1.523(8) Angstroem, and the average FSF and FSN bond angles are 94.0(5) and 100.2(6) deg.The SNS bond angle is 121.1(6) deg.The vibrational spectrum of (SF2)2NAsF6 is reported.
- Brooks, Wendell V. F.,MacLean, Gregory K.,Passmore, Jack,White, Peter S.,Wong, Chi-Ming
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p. 1961 - 1968
(2007/10/02)
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- Negative ion-molecule reactions of SF4
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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.
- Babcock, Lucia M.,Streit, Gerald E.
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p. 3864 - 3870
(2007/10/02)
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- Rate constants and vibrational energy disposal for reaction of H atoms with Br2, SF5Br, PBr3, SF5, and SF4
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Rate constants and initial HBr and HF product distributions for the title reactions were measured in a fastflow apparatus using infrared chemiluminescence techniques.The spectra were interpreted using a new set of Einstein coefficients for HBr, which are listed in the Appendix.The rate constants for HBr(υ>/=1) and HF(υ>/=1) formation, relative to the H+Cl2 reaction, are 3.3, 0.39, 0.50, 3.4, and 0.003, for Br2, SF5Br, PBr3, SF5, and SF4, respectively.This directly measured Br2 rate constant supports the smaller values that heve been estimeted in the literature.The initial HBr vibrational distribution (υ1:υ2:υ3:υ5=0.03:0.20:0.40:0.31:0.06) from H+Br2 corresponds to V>=0.49.The observed HBr vibrational distributions (υ1:υ2:υ3:υ4) are 0.28:0.43:0.23:0.06 and 0.63:0.24:0.13 for SF5Br and PBr3, respectively.The SF5Br results are close to the initial distribution and give V>=0.36.The low vapor pressure of PBr3 limited the and high was required to observe HBr emission; correcting the observed distribution for vibrational relaxation gives V ca. 0.47.These V > values include estimates for HBr(υ=0).Based upon the highest HBr level observed from SF5Br and PBr3, D0(Br-SF5)0(Br-PBr2)-1.The HF vibrational distributions from SF5 and SF4 decline with increasing υ, which suggests that these reactions proceed via a long-lived complex.For these cases the formation of HF(υ=0) is important, and significant corrwections must be made to the HF(υ>/=1) formation constants to obtain the total HF formation rate constants.The rate constants and energy disposal data are used to discuss models and compare the H+Br2 reaction to H+Cl2 and F2.
- Malins, R. J.,Setser, D. W.
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p. 5666 - 5680
(2007/10/02)
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- The reactions of uranium hexafluoride with hydrogen sulfide and with carbon disulfide
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Uranium hexafluoride reacts with hydrogen sulfide at 25° to produce uranium tetrafluoride, sulfur tetrafluoride, and hydrogen fluoride. Uranium hexafluoride reacts with carbon disulfide vapor at 25° to produce uranium tetrafluoride, sulfur tetrafluoride, bistrifluoromethyl disulfide [(CF3)2S2], and bistrifluoromethyl trisulfide [(CF3)2S3], and at elevated temperatures the reaction also produces sulfur hexafluoride and tetrafluoromethane, CF4. When uranium hexafluoride vapor reacts with carbon disulfide vapor at 25° in the presence of helium as a diluent, the favored perfluoroalkyl product is bistrifluoromethyl trisulfide. Uranium hexafluoride is compared with other metal fluorides with respect to their reactions with carbon disulfide.
- Trevorrow,Fischer, Jack,Gunther
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p. 1281 - 1284
(2008/10/08)
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- New syntheses of diboron tetrafluoride
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Diboron tetrafluoride has been prepared by the reactions of sulfur tetrafluoride with boron monoxide, tetrahydroxydiboron, or tetraethoxydiboron.
- Brotherton,McCloskey,Manasevit
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- The preparation of difluoroamino sulfur pentafluoride
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Difluoroamino sulfur pentafluoride (SF5NF2) has been synthesized by the ultraviolet irradiation of N2F4 and sulfur tetrafluoride or sulfur chloride pentafluoride, or by the thermal reaction of N2Fsub
- Logothetis,Sausen,Shozda
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p. 173 - 175
(2008/10/08)
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