V.D. Klimov

Infrared spectroscopy of fluoride molecules in noble gas solutions. I: Octahedral molecules

Infrared spectra of the spherical top molecules XF6 (X = S, U, Mo, W) dissolved in liquefied argon, krypton and xenon have been studied. It is shown that the observed Lorentz shape of the bands results from two processes: vibrational dephasing and rotational diffusion. In contrast to fundamental transitions A1g - F1u, for the (v 2 + v 3) state it has proved necessary to apply two limiting cases: when the anharmonic level splitting ΔE anh is much greater than the Coriolis coupling, and when ΔE anh is small relative to the Coriolis coupling. Measured values of band halfwidths are compared with the theoretical values, obtained with the help of a rotational diffusion model. It is concluded that, in contrast to SF6, vibrational dephasing and intermolecular interactions contribute essentially to the formation of band contours of heavy metal hexafluorides. The second moment for the (v 2 + v 3) band has been estimated. The characteristic times of angular momentum correlation for SF6, UF6, MoF6 and WF6 molecules i...

Investigation of uranium hexafluoride hydrolysis kinetics by laser HF analyzer

Abstract Uranium hexafluoride is used on a large scale in industry for the separation of uranium isotopes. Aside from scientific interest, the information about the kinetics of the UF 6 hydrolysis reaction is necessary for predicting its behaviour when uranium hexafluoride gets into the environment. The reaction rate between UF 6 and H 2 O was measured in a spectrophotometric cell by the decrease with time of the radiation He-Ne laser intensity at the wave length of λ=2,3952 μk which is absorbed selectively by HF molecules (band 1R5) [V. D. Klimov, Ya.M. Kravetz, A.P. Pashchenko, A.A. Tishchenko and T.A. Udalova, J. Fluorine Chem., 54 (1991) 343]. The reaction was examined under the low pressure of the reagents (∑p ⩽ torr) and at atmospheric pressure in moist air with a 5–10 fold excess of H 2 O. The experimental data were treated assuming that the hydrolysis reaction is consecutive and proceeds in two stages: UF 6 +H 2 O UOF 4 +2HF (1) UOF 4 +H 2 O UO 2 F 2 +2HF (2) It was found that the constant of the limiting stage (1) equals (4±4)·10 −18 cm 3 ·s −1 .

IR-Spectroscopy of inorganic fluorides dissolved in liquefied noble gases

Abstract Vibrational spectra of solutions in liquefied noble gases at low temperatures gives wide scope for obtaining information concerning molecules being studied. The main aspect of interest with liquefied noble gases is their high inertness and transparency from the vacuum ultraviolet up to the radio-frequency region. Thus with the obvious advantage of the high accuracy of determining main molecular parameters (frequencies of vibrational bands, force constants, isotopic shifts, etc.), the cryogenic solution method can be used for the study of extremely aggressive and unstable chemical compounds, which includes a considerable number of inorganic fluorides. Moreover, the mentioned method can be used to study intermediate molecular systems formed by complex processes and photochemical reactions and to determine the symmetry, stoichiometry and structure of these molecules. The present work summarises the results of the study of IR spectra of M F 6 ( M =S, U, Mo, W), ClF n ( n =3, 5), C R 3 SiF 3 ( R =H, Cl), XeF m ( m =2, 4, 6), CrO 2 F 2 , PF 3 , etc., solutions in liquid Ar, Kr and Xe. Regular contour formation is observed and a number of spectroscopic parameters are determined. The structural peculiarities of the studied molecules in liquid noble gases are discussed.

Investigation of ClOF3HF interaction in liquid Xe

Abstract The system ClOF3HF (T=293 K) was studied formerly by means of Raman spectroscopy [Sh. Sh. Nabiev, I.I. Ostroukhova, A.V. Ryzhkov, V.B. Sokolov and S.N. Spirin, J. Fluorine Chem., 54 (1991) 333]. On the basis of polarization measurement results it was shown that in this system strong intermolecular interactions are accompanied by considerable ionization of the solute. The present work is devoted to the investigation of infrared spectra of ClOF3HF system in liquid xenon solution at T=180 K. The bands corresponding to ClF, ClO and HF bond vibrations were studied. The mechanisms of ClOF2+ and HF2− band contour formation were discussed.

IR-Cryospectroscopy as a method for trace analysis of molecular impurities in inorganic fluorides

Abstract Inorganic fluorides have been widely used lately as initial reagents in a series of technological processes connected with the production of substances of high purity. The fine purification of inorganic fluorides calls for elaborating analytical methods for traces of molecular impurities in gas phases. One of the most promising methods of fluoride quantitative analysis is cryogenic IR-spectroscopy, which is based on the ability of most gases to dissolve in liquid noble gases. The low temperature of solutions in liquefied Ar (90 K), Kr (130 K), Xe (180 K) as well as the inertness of the solvents considerably simplify the molecular vibrational spectra at the expense of the suppression of ‘hot’ bands and the retardation of rotational motion. As a result, the rotation-vibration bands of the substance being analyzed, as well as the bands of the impurities, are observed in IR spectra as very narrow lines with half- width Δν 1 2 =0.3−3 cm −1 . That is why the analysis sensitivity at an average spectral resolution of 0.5–1.0 cm −1 increases 50–100 times, and as compared with anaysis of the gas mixtures at P=1 atm with spectral resolution≅0.1 cm −1 , increases 5–10 times. At the present time we have data on the analytical bands of most widespread impurities in inorganic fluorides, such as CF 4 , SiF 4 , NO, N 2 O, H 2 O, CO, CO 2 , OF 2 , NF 3 , freons, etc., obtained with pinpoint accuracy. Further, there are data on the solubility of the mentioned impurities as well as on the solubility of many fluorides in liquefied noble gases. The limits of detection of molecular impurities in inorganic fluorides for cryostates with the length of optical path L≅1 m were 10 −4 –10 −6 %. Methods of increasing the sensitivity of cryospectroscopy analysis are discussed.

Cryospectroscopic analysis of individual xenon fluorides

Abstract Considerable attention has been paid lately to pure fluorination agents, in particular xenon fluorides, which are usually produced as a result of interaction of high purity xenon and fluorine activated thermally, photochemically, plasmochemically or by other methods. However, the production of individual xenon fluorides is somewhat difficult because as a rule a mixture of XeF 2 , XeF 4 and XeF 6 usually forms in the reactor. Moreover, whereas the choice of the optimal conditions of synthesis yields practically pure XeF 2 and XeF 6 , a small quantity (10 −2 –10 −3 mol. part) of XeF 2 and XeF 6 impurities forms during XeF 4 production, even under optimal conditions. Thus it is necessary to control the composition of synthesized fluorides XeF n ( n =2, 4, 6) directly in the reaction zone. IR spectroscopy of XeF 4 solutions in liquid xenon at T=180 K was used to solve this problem. Spectra registration was carried out in the range 700–500 cm −1 (L cryo =10 cm). In xenon fluorides spectra the bands of fundamental modes ν 3 (XeF 2 )=544.7 cm −1 , ν 6 (XeF 4 )=571.8 cm −1 , ν(XeF 6 )=596 cm −1 were registered and identified. Measurement of the xenon fluorides solubility in liquid xenon gave the following results: XeF 2 =1.4·10 −5 mol/l, XeF 4 =6·10 −6 mol/l, XeF 6 =4·10 −4 mol/l. The study of XeF n infrared spectra in the region of fundamental modes showed that their main bands are distant (Δν≊25 cm −1 ) with half-width Δν 1 2 ≊5–6 cm −1 . Therefore, there is a real possibility of carrying out quantitative analysis for the presence of other xenon fluorides in individual XeF n . Estimation showed that the use of a cryostat with an optical length of 50–100 cm gives the possibility to detect the impurities of xenon fluorides in individual form of XeF n in quantities 10 −3 –10 −5 mol. part.

Infrared spectroscopy of XeF2, XeF4 and XeF6 molecules in liquid-xenon solution

Abstract The infrared spectra of XeF2, XeF4 and XeF6 molecules were investigated in liquefied noble gas solutions. It is shown that incryogenic solution (liquid Xe, T=180 K) XeF2 and XeF4 molecular structure weak distortion due to the effective solute-solvent interaction takes place. The anharmoniciti constants X13 (XeF2) and X46 (XeF4) were computed. It was found that the increase of XeF6 concentration in a liquid xenon solution causes both the decreas of the number of monomers XeF6 with the strong 596 cm−1 band and the polymers (XeF6)n formation characterised by intensive band group in 620–640 cm−1 region. The equilibrium constants were computed for reaction n(XeF6) = (XeF6)n (n=2,4). It is shown that in contrast to classical octahedral molecules such as SF6, UF6 and others [1], polymerization of xenon hexafluoride is followed by the stabilization of non-rigid structure of this molecule at the expense of the mobiliti decrease of the fluorine atoms which results in the decrease of XeF bond rigidity. The results of the studies on IR spectra of XeF6 in liquid-xenon solution over the wide frequency range 400–2000 cm−1 led to the conclusion that the geometrical configuration of an octahedron distorted to a C3v-symmetry is the basic one for xenon hexafluoride.

Investigation of thermal decomposition of (NO2)2NiF6

Abstract The thermal decomposition of (NO2)2 NiF6 in a closed system has been investigated in the temperature range from 393 to 443K. The decomposition rate has been investigated by measuring the increase of the total pressure of the gaseous decomposition products of F2 and NO2F in the IR spectrophotometric cell. The concentration variation of NO2F has been registered using spectrophotometric technique on the band 572 cm−1 V 3A1. The analyses of the experimental results proved that the decomposition of (NO2)2NiF6 might be described in terms of the total reaction The mathematical simulation of the process has been carried out with the aid of a computer. Being calculated in terms of Arrhenius dependence 1nk = f(1/T) the effective activation energies of the stages mentioned above proved to be equal to E1=(38 ± 7) KJ/mol, E2= (46 ± 8) KJ/mol and 33= (4 ± 1) KJ/mol. The decomposition reaction of (NO2)2 NiF6 into fluorine nitrile and nickel tetrafluoride (1) is the limiting state of the thermal decomposition process.

Synthesis and properties of binuclear decakis (Trifluorophosphine) technetium(O) Complex

Abstract Decakis (trifluorophosphine) technetium (O) Tc 2 (PF 3 ) 10 has been synthesized by means of cryochemical method. Compound Re 2 (PF 3 ) 10 described in literature previously [1] has been obtained by using the same technique. The synthesized trifluorophosphine complexes of Tc and Re which are close chemical analogues have similar physical - chemical properties. Both compounds have white colour. They are hydrolysed in the wet air. Vapour pressure of Tc 2 (PF) 10 is (6±3) . 10 -3 torr at 293K. When heated up to 550K Tc 2 (PF 3 ) 10 decomposes with Tc and PF 3 being liberated. The Tc 2 (PF 3 ) 10 bands 455 vw, (492 ms, 498 ms) (ν 2 PF 3 ), 734 sh, 856 s (ν 3 PF 3 ), 896 s (ν 1 PF 3 ), 1016 w.br., 1122 w.br., 1237 w.br. and the Re 2 (PF 3 ) 10 bands 460 vw, {492 ms, 508 ms} (ν 2 PF 3 ), 744 sh, 859 s (ν 3 PF 3 ), 893 s (ν 1 PF 3 ), 1021 w.br., 1155 w.br., 1261 w.br., cm -1 were detected in infrared spectra of solid samples. The bands located above 1000 cm -1 were identified to be phosphide Tc and Re and phosphorus oxides impurities. The masses corresponding to M + 2 , M(PF 3 ) + x , M 2 P(PF 3 ) + y , MPF (PF 3 ) + y , M 2 PF(PF 3 ) + y ions, where M = Te, Re, X = 0+4, Y = 0+8 for Tc complex and X = 0+4, Y = 0+3 for Re complex were present in mass spectra of the compounds synthesized.