Longuet-Higgins groups of XeF6

A complete permutational analysis of the XeF₆ dynamics is presented. The Longuet-Higgins group for each mode of rearrangement is obtained. On the basis of the splitting scheme of rigid molecule levels and statistical weights and selection rules for the non rigid molecule levels, it appears that transverse digonal twists and turnstile mechanisms have the same spectroscopic effects as the BPR -6 mechanisms. Hence, the previous interpretation of IR and Raman spectra is consistent with tunneling through transverse digonal twists and turnstile mechanisms as well as through BPR -6.     

Relativistic molecular wavefunctions: XeF2

A new method is presented to calculate binding energies and eigenfunctions for molecules, using the relativistic Dirac hamiltonian. A numerical basis set of four component wavefunctions is obtained from atom-like Dirac-Slater wavefunctions. A discrete variational method has been developed and applied to the linear XeF₂ molecule.     

On the preparation of fluorine-18 labelled XeF(2) and chemical exchange between fluoride ion and XeF(2)

A recent report claims to have prepared [18F]XeF2 by exchange between a large stoichiometric excess of XeF2 and no-carrier-added 18F-, as salts of the [2,2,2-crypt-M+] (M = K or Cs) cations, in CH2Cl2 or CHCl3 solvents at room temperature. Attempts to repeat this work have proven unsuccessful and have led to a critical reinvestigation of chemical exchange between fluoride ion, in the form of anhydrous [N(CH3)4][F] and [2,2,2-crypt-K][F], and XeF2 in dry CH2Cl2 and CH3CN solvents. It was shown, by use of 19F and 1H NMR spectroscopies, that [2,2,2-crypt-K][F] rapidly reacts with CH3CN solvent to form HF2-, and with CH2Cl2 solvent to form HF2-, CH2ClF, and CH2F2 at room temperature. Moreover, XeF2 rapidly oxidizes 2,2,2-crypt in CH2Cl2 solvent at room temperature to form HF and HF2-. Thus, the exchange between XeF2 and no-carrier-added 18F- reported in the prior work arises from exchange between XeF2 and HF/HF2-, and does not involve fluoride ion. However, naked fluoride ion has been shown to undergo exchange with XeF2 under rigorously anhydrous and HF-free conditions. A two-dimensional 19F-19F EXSY NMR study demonstrated that [N(CH3)4][F] exchanges with XeF2 in CH3CN solvent, but exchange of HF2- with either XeF2 or F- is not detectable under these conditions. The exchange between XeF2 and F- is postulated to proceed by the formation of XeF3- as the exchange intermediate.     

Nonrigid molecule effects on the energy levels of XeF6

The geometric and electronic structure of XeF₆ is not yet fully understood, even though most of the means of structure determination available to the chemist have been employed in an effort to describe the molecule. We suggest that many of the experimental anomalies and theoretical difficulties arise from the possibility of rapid polytopal rearrangement in this system, and put forward in this report an analysis which accommodates the experimental data. We show that easy rearrangement produces substantial splittings in rigid-molecule energy levels, and with the aid of Longuet-Higgins group theory developed expressly for flexible molecules, compute energy-level schemes for a set of plausible rearrangement modes. By appropriate choice of parameters specifying the extent of splitting, we match the reported infrared and Raman spectra, and their temperature dependence. The puzzling “time lag” in the Raman (but not the infrared) spectrum is tentatively ascribed to selective relaxation of Raman-active vibrational modes.     

Studies on the use of XeF2 as digestion reagent

A digestion procedure was developed for the determination of selected elements (Al, Ba, Ca, Ce, Cd, Co, Cr, Cu, Fe, La, Mg, Ni, Sr, Pb, Zn) in sediments using XeF₂. The use of XeF₂ has some interesting features but this reagent should be handled only under dry gas which is a severe limitation of the methodology. In a first step the sediment sample (0.1 g) is dried (120 °C) and digested by XeF₂ (1.5 g) in the vapor phase (190 °C; 9 × 10⁶ Pa). Then the dry residue is dissolved in aqua regia and the solution digested at high pressure once again (aqua regia digestion). Subsequently the digested solution is diluted with sub-boiling distilled water and is ready for the analysis by ICP-MS. The sediment standard CRM 320 was analyzed to verify the procedure. A comparison of the results with those obtained by the normally used fluoric acid digestion showed that the recovery rates of each investigated element agreed within a confidence interval of 95%, except Cr. The recovery rate of Cr was lower for the XeF₂ digestion than for the fluoric acid digestion by more than 5%. Further studies were focussed on the possible digestion of SiC by XeF₂ as first step for the trace element determination. In the gaseous reaction products Si could be detected by ICP-MS which gives evidence to a decomposition of SiC. A digestion procedure for small Si samples (0.010 g) was developed. Detection limits (DL) determined for selected elements of analytical interest (Al, Ca, Cd, Cr, Co, Cu, Fe, Mg, Ni, Pb) were between 1 to 12 ng/g. For most of the elements this is an improvement in comparison to the HF vapor phase digestion. The verification of the method was carried out with GFAAS. Received: 17 February 1999 / Revised: 15 June 1999 / Accepted: 17 June 1999     

Bonding and electronic structure of XeF3-

The xenon-fluoride bond dissociation energy in XeF3- has been measured by using energy-resolved collision-induced dissociation studies of the ion. The measured value, 0.84 +/- 0.06 eV, is higher than that predicted by electrostatic and three-center, four-electron bonding models. The bonding in XeF3- is qualitatively described by using molecular orbital approaches, using either a diradical approach or orbital interaction models. Two low-energy singlet structures are identified for XeF3-, consisting of Y- and T-shaped geometries, and there is a higher energy D3h triplet state. Electronic structure calculations predict the Y geometry to be the lowest energy structure, which can rearrange by pseudorotation through the T geometry. Orbital correlation diagrams indicate that that ion dissociates by first rearranging to the T structure before losing fluoride.     

Freezing in resonance structures for better packing: XeF2 becomes (XeF+)(F-) at large compression

Recent high-pressure experiments conducted on xenon difluoride (XeF(2)) suggested that this compound undergoes several phase transitions up to 100 GPa, becoming metallic above 70 GPa. In this theoretical study, in contrast to experiment, we find that the ambient pressure molecular structure of xenon difluoride, of I4/mmm symmetry, remains the most stable one up to 105 GPa. In our computations, the structures suggested from experiment have either much higher enthalpies than the I4/mmm structure or converge to that structure upon geometry optimization. We discuss these discrepancies between experiment and calculation and point to an alternative interpretation of the measured cell vectors of XeF(2) at high pressure. At pressures exceeding those studied experimentally, above 105 GPa, the I4/mmm structure transforms to one of Pnma symmetry. The Pnma phase contains bent FXeF molecules, with unequal Xe-F distances, and begins to bring other fluorines into the coordination sphere of the Xe. Further compression of this structure up to 200 GPa essentially results in self-dissociation of XeF(2) into an ionic solid (i.e., [XeF](+)F(-)), similar to what is observed for nitrous oxide (N(2)O) at high pressure.     

The use of XeF2 for preparation of azepins

Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1841–1842, October, 1994.     

First detection of a selenenyl fluoride ArSe-F by NMR spectroscopy: the nature of Ar2Se2/XeF2 and ArSe-SiMe3/XeF2 reagents

Arylselenenyl fluorides ArSeF are obtained from diselenides Ar2Se2 or arylselenotrimethylsilanes ArSe-SiMe3, and XeF2. They are detected by low-temperature 19F and 77Se NMR spectroscopy. Substitution in the ortho position of the aromatic ring to provide electronic or steric protection is a requirement for their formation. ArSe--F compounds decompose according to 3 ArSe-F-->[ArSe-SeF2Ar]+ArSe-F-->ArSeF3+Ar2Se2. Reaction energies for this disproportionation as well as that of the sulfur and tellurium homologues have been calculated with MP2, CCSD(T,) and B3 LYP methods. They were found to be increasingly exothermic in the sequence S相似文献   

On the existence of the trifluoroxenate (II) ION,XeF3-: Comments on “the ‘base catalyzed’ fluorination of SO2 by XeF2”

Conflicting data on the existence of the trifluoroxenate (II) ion, XeF₃^-, is analyzed. In particular, lack of isotope exchange and new spectroscopic lines in XeF₂ + F^- reactions, negative ion mass spectra of xenon fluorides and the “‘Base Catalyzed’ Fluorination of SO₂ by XeF₂” are discussed.     

A study of the XeF molecule by atomic beam scattering with magnetic analysis

Absolute total cross sections for scattering of fluorine atoms by xenon have been measured in the 0.9–2.0 km s^? velocity range. Information is obtained on the long-range interaction and, using a technique for magnetic analysis of substates of F atoms, a characterization is given for the bonding in the two lowest excited states of XeF.     

XeF4 as a Ligand for a Metal Ion

Noble molecule : [Mg(XeF₂)(XeF₄)](AsF₆)₂ is the first coordination compound in which XeF₄ acts as a ligand to a metal center. It is also the first known compound, in which XeF₂ and XeF₄ are simultaneously coordinated to the same metal center (see structure; purple Xe, green F, gray Mg, yellow As).

     

Spin–orbit and dispersion energy effects in XeF

Spin–orbit and dispersion energy contributions to the energy curves of XeF are examined. A rapid variation in the spin–orbit coupling with internuclear separation is found for both the ground and excited states. This result can explain the experimentally observed ordering of the ionic excited states when the spin–orbit perturbation couples ²σ and ²π energy curves obtained by both all-electron and effective core potential (ECP ) calculations at the first-order configuration interaction (FOCI ) level of accuracy. Damped dispersion energy contributions to the ground-state energy curve are shown to be comparable to the charge transfer contribution. The energy curve for XeF is in reasonable agreement with experimental results and a calculation of the analogous XeCl curve confirms the qualitative correctness of the calculation. The energy curves and transition moments were then applied to two problems related to the efficiency of the XeF laser. Photodissociation of the X state provides a means of removing a bottlenecked vibrational level but a calculation of the radiative transition probability between the X and A states finds the cross section is too small to yield rates competitive with collisional deactivation. The bottlenecked state may also be removed by electron dissociative attachment but the calculated energy curves for the X states of XeF and XeF^? do not cross at a low energy indicating a small cross section.