Near-UV photodissociation of gaseous UF6 in the presence of H2

Mixtures of UF₆ and H₂ in different ratios have been irradiated at 360 and 400 nm by means of a filtered mercury lamp. A significant pressure drop has been observed at both excitation wavelengths due to the dissociation of UF₆ into UF₅+ F. A very high dissociation quantum yield has been found.     

SF6-sensitized dissociation of UF6 with a pulsed CO2 laser

The dissociation of UF₆ sensitized by SF₆ excited with a pulsed CO₂ laser in the presence of H₂ and CO as scavengers has been investigated. In the SF₆-UF₆-H₂ system the dissociation yields have been determined as a function of the laser frequency, the fluence, and H₂ partial pressure. A maximum dissociation yield has been found at a laser frequency of 935 cm^?1. No obvious dissociation of UF₆ was observed in the UF₆-SF₆ system without F-atom scavengers.     

Development of new methods for the reduction of UF6

Methods for the preparation of UF₅ are discussed with respect to the formation of β-UF₅. The reduction of UF₆ by HBr in liquid HF /1/ can be used to synthesize pure β-UF₅ even if greater amounts are required.Details of the direct photolysis of UF₆ without scavenger /2/ are presented. In an advanced version a simplified photo-reactor is used which consists of a stainless steel vessel with a diameter of 100 mm and a volume of about 3 liters. UV-light of a 1000 W super high pressure mercury lamp is used to photolyze about 50 g of high purity UF₆ within 12 h, giving pure β-UF₅ in about 90 % yield without intermediately removing the F₂ formed.Two simple new methods have been developed to synthesize β-UF₅. UF₆ is reduced by H₂ in liquid anhydrous HF at room temperature. This reaction which is hindered kinetically at room temperature can be catalyzed by metallic Au which is applied as a foil in the stirred reaction mixture.In addition, it was found that anhydrous HCl catalyzes the reaction, too. 200 mbar of HCl were added, together with 4 bar H₂, to UF₆ in liquid HF, and the reaction mixture was magnetically stirred for 66 hours. β-UF₅ could be obtained in 91 % yield as a very pure product. This latter method is recommended for large scale production of β-UF₅.Reactions of UF₆ with other reducing agents like HCl, SO₂, and CO in liquid HF were studied. These reactions give poor yields or impure products.UF₆ yields with CO and Au in the presence of HF a carbonyl compound of Au with the very high ν_CO at 2205 cm^?1. Analytical and spectroscopic data suggest the formula Au(CO)₂U₂F₁₁.     

Simultaneous vibration-vibration and vibration-translation transitions in H2 + D2 at high collision energies

The coupling between VV and VT transitions in H₂(2) + D₂(0) → H₂(1) + D₂(1) and D₂(2) +H₂(0) → D₂(1) + H₂(1) at high collision energies is investigated by use of the solution of the Schrodinger equation of motion. The coupling is sufficiently important that the energy exchange processes cannot be described by the VV mechanism alone.     

The temperature dependence of the HO2 + HO2 reaction

The temperature dependence of the rate constant for the reaction HO₂ + HO₂ → H₂O₂ + O₂ (2k₁) has been determined using flash photolysis techniques, over the temperature range 298–510 K, in a nitrogen diluent at a total pressure of 700 Torr. The overall second order state constant is given by k₁ = (4.14 ± 1.15) × 10^?13 exp[(630 ± 115)/T] cm³ molecule^?1 s^?1, where the quoted errors refer to one standard deviation. This result is compared with previous findings and the negative activation energy is shown to be consistent with the observation that the rate constant is pressure dependent at 700 Torr.     

Vapour-liquid equilibrium data for the systems C2H6 + N2, C2H4 + N2, C3H8 + N2, and C3H6 + N2

High pressure vapour-liquid equilibrium data for the C₂H₆ + N₂, C₂H₄ + N₂, C₃H₈ + N₂, and C₃H₆ + N₂ systems are presented. The data are obtained isothermally in the range from 200 K to 290 K. For each point of data, temperature, pressure and liquid and vapour phase mole fractions are measured.Values for the vapour phase mole fractions are calculated from the obtained pressure, temperature and liquid phase mole fractions. The calculated values are compared with the experimental results, and it is found that the average mean deviation between calculated and experimental mole fractions is less than 0.009 for the systems considered in this work.     

Photodissociation reaction CO−3

Photodissociation reaction CO^?₃ + hv → CO₂ + O^? has been observed at seven photon energies between 2.35 and 2.71 eV using a drift tube mass spectrometer and an argon ion laser. The total cross sections for the destruction of CO^?₃ due to photons of these energies have been measured, and it is concluded that essentially all of this destruction is due to photodissociation. The photodestruction of CO^?₃.H₂O has also been observed at four photon energies.     

Sensitized multiphoton dissociation of UF6 IN SF6-UF6 mixtures by a tea CO2 laser

UF₆ undergoes decomposition in the presence of SF₆ when mixtures of both are irradiated with a TEA CO₂ laser. The mechanism for UF₆ decomposition may involve vibrational energy transfer from excited SF₆ and laser absorption from the same laser pulse by excited UF₆ in its vibrational quasi-continuum     

Circular dichroism of Mn2+ ions in α-Zn(H2O)6SeO4 crystal

The circular dichroism (CD) of Mn²⁺ ions in α-Zn(H₂O)₆SeO₄. crystal has been measured at 77–300°K. CD lines associated with the spin forbidden transition ⁶A₁ → ⁴A₁,⁴_aE are observed, and compared with uniaxial rotational strengths calculated on the basis of ligand field theory. The CD bands of Mn²⁺ and Ni²⁺ simultaneously doped into a Zn(H₂O)₆SeO₄ crystal have the same sign, which accords with a theoretical prediction.     

Theoretical calculations of the electronic structure and optical transitions of UF6 and UF5

The self-consistent-field Xα scattered wave (SCF Xα SW) approach to molecular orbital theory has been applied to the UF₆ molecule and to an assumed structure of UF₅ (in C_4v symmetry) to determine their electronic structures and optical transitions.     

Rotating frame spin-lattice relaxation through anisotropic chemical shift in polycrystalline UF6

A minimum in the temperature dependence of the ¹⁹F rotating frame spin-lattice relaxation time T_1? in polycrystalline UF₆ has been observed which enables one to determine the correlation time for slow reorientations of the UF₆ octahedra directly. The dependence of the depth of the T_1? versus temperature minimum on the external magnetic field H₀ at a fixed value of the rotating field H₁ provides an independent proof that fluctuations of the ¹⁹F screening constant tensor significantly contribute to the fluorine spin-lattice relaxation rate in this system.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

Composes d'addition entre les pentafluorures d'uranium et d'antimoine,preparation des composes UF5. n SbF5 (n = 1 ou2)

The adduct UF₅.2SbF₅ has been obtained from the reaction of UF₅ with SbF₅ and the reaction of UF₆ with SbF₅ in the presence of freon 114. From this preparation and also from studies on UF₆, SbF₅ solutions, the fluorinating properties of UF₆ were found to be enhanced by the presence of SBF₅. An x-ray diffraction study has shown that crystals of UF₅.2SbF₅ are monoclinic, space group P2₁/c, with unit cell dimensions a = 8.036(3) Å ; b = 14.112(13) Å ; c = 10.028(17) Å ; β = 96.91(7)°.The adduct UF₅.SbF₅ is obtained by thermal decomposition of UF₅.2SbF₅.     

Conversion de UF6 appauvri en U3O8

Uranium hexafluoride (UF₆), to or from isotopic enrichment plants is stored and transported, as a solid, in tanks containing 2 to 12 metric tons of material. Sampling must be carry out after complete melting obtained by heating of the tank. This sampling process is difficult and hazardous by risks of local solidification (sealing), of reaction with air moisture (Fluorhydric Acid, highly corrosive and toxic is formed), of chemical and radioactive contamination (in case of leaking), of loss of expensive material (especialy if enriched UF₆), and of over-filling of sampling pot (possible domage during warming up of itagain).The described new device was concepted and developed by COGEMA Laboratories and is used for two years in sampling facilities of enrichment plant of PIERRELATTE. It permits to warrant sample validity and eliminate all the hereabove risks.It allows seeing and adjusting volume of the samples and their flow, and permits measurement of temperature and pressure, specified for UF₆.This new device is usable for many others materials which present some risks and difficults, as Fluorine and its derivates, chlorine, liquefied inflammable gases etc.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

Experimental study of the D + H2(ν = 1) reaction

The D + H₂(ν = 1) reaction, D + H₂(ν = 1) → K_a HD(ν = 1) + H, → K_n HD(ν = 0) + H, → K_r D + H₂(ν = 0) has been studied. The measurements were made in a flow-tube apparatus at 300 K. Vibrationally excited H₂ was generated in a furnace and D atoms in a microwave discharge. EPR and thermometric techniques were used for the detection of D and H atoms and H₂(ν = 1). The product branching rate constants (in CM³/Molecule s) were found to be K_a = (10.7 ± 4.1) × 10^?13. K_n = (5.4 ± 2.7) × 10^?13, K_r, < 2.7 × 10^?13.     

Orbital ground state inversion in [Fe(H2O6](CIO4)2

Mössbauer spectroscopy in external magnetic fields has been used to measure the signs of the principal components of the electric field gradient V_zz in the two forms of [Fe(H₂O)₆)(C10₄)₂. The signs are V_zz negative for the (B) with ΔE_B = 1.4 mm/sec. This implies a trigonally distorted ligand field and the transition (A) → (B) corresponds to compression → elongation with respect to the trigonal axis.     

(p, ϱ, T) for {(1−x)C6H6 + xC6D6} and {(1−x)C6H6 + xC6F6} in the range 298 to 373 K and 0.1 to 400 MPa

The behaviour of (p, ?, T) for C₆H₆, C₆F₆, and five mixtures, and of C₆D₆ and (0.5C₆H₆ + 0.5C₆D₆) has been determined at 298.2, 323.2, 348.2, and 373.2 K, and from 0.1 MPa, or saturation pressure, to the point of onset of solidification or to 400 MPa. The experimental results are tabulated and the isothermal densities are represented by a polynomial equation for the secant bulk modulus in terms of the pressure. The temperature and pressure dependence of the molar excess volume is described.     

Fourier transform IR spectroscopic observation of pernitric acid formed via HOO + NO2 → HOONO2

Kinetic and spectroscopic evidence has been found for the formation of pernitric acid via HOO + NO₂ → HOONO₂ using Cl-atom sensitized oxidation of H₂  NO₂ mixture and a Fourier transform IR spectroscopic detection method.     

Temperature dependence of the probabilities of VV energy exchange between H2 and DCl

The temperature dependence of the removal of the vibrational energy of H₂ by DCl in H₂(1) + DCl(0) has been investigated over the range of 300–3000 K. The energy transfer probability of H₂(1) + DCl(0) → H₂(0) + DCl(1), where the vibrational energy of H₂(1) is removed by both the vibrational and rotational motions of DCl(0), is found to be strongly temperature dependent and increases with temperature closely following the relation log P α T^1/3. Over the temperature range it changes by two orders of magnitude. The probability of the near-resonant process H₂ (1) + DCl(O) → H₂(0) + DCl(2) is very close to that of the former at 300 K, but it increases only slightly as the temperature is raised to 3000 K. The sum of the probabilities of these two processes at 300 K is 3.4 × 10^?5, which agrees with the experimental value of 3.95 × 10^?5.