Showing papers on "Uranyl published in 1976"
TL;DR: In this article, the low-temperature single-crystal optical absorption spectrum of Cs2UO2Cl4 is reported in six different polarizations and measurements have also been made on the 18O compound Zeeman-effect measureme
Abstract: The low-temperature single-crystal optical absorption spectrum of Cs2UO2Cl4 is reported in six different polarizations Measurements have also been made on the 18O compound Zeeman-effect measureme
139 citations
01 Jan 1976
TL;DR: In this paper, the influence of charge transfer and rydberg (f n−1 d) states on the luminescence of lanthanides and actinides (more specifically hexavalent uranium) is demonstrated.
Abstract: The influence of charge-transfer and rydberg (f n−1 d) states on the luminescence of lanthanides and actinides (more specifically hexavalent uranium) is demonstrated. Optical transitions between the ground state and these excited states, and their dependence on electron configuration and crystallographic surroundings of the complex involved, are discussed first. The influence of charge-transfer and f n−1 d states on emission spectra is dealt with. It is shown that the characteristics of emission spectra are often very sensitive to the energetic position of these states. Even more drastic is their influence on the temperature quenching of these emissions. Especially the case of the Eu3+ ion in oxysulfides is reviewed extensively. Direct feeding of the 5D levels of Eu3+ by charge-transfer states occurs, but the reverse process is also possible. The spectral position of transitons to charge-transfer and f n−1 d states can influence energy transfer probabilities. Metal ion-metal ion charge transfer states are also of great importance in this field. Finally some luminescence properties of hexavalent uranium are discussed. It is shown that often this emission is due to an octahedral UO 6 6− group and not to the well-known uranyl (UO 2 2+ ) group. Charge-transfer states involving 5/ and possibly 6d levels determine the dependence of the emission characteristics on the host lattice.
117 citations
TL;DR: In this article, the effects of secondary ligands on the electronic structure of uranyl, UO2++, were investigated in a perturbing point ion model, making use of the relativistic Dirac-Slater molecular orbital (MO) approach.
Abstract: The effects of secondary ligands on the electronic structure of uranyl, UO2 ++, are investigated in a perturbing point ion model, making use of the relativistic Dirac–Slater molecular orbital (MO) approach. Variation of ’’crystal‐field splittings’’ with primary U–O bond length is explored; relaxation of the uranyl MO’s is taken into account by self‐consistent iterations. The theoretical splittings are found to agree rather well with the x‐ray photoemission spectroscopy (XPS) data of Veal et al. Comparison is made with optical data and reasons are given for the poor agreement.
81 citations
78 citations
TL;DR: In this article, the quenching of the uranyl ion by other metal ions has been studied in aqueous solution, and the correlation of the logarithm of the rate with the metal ion ionization potential suggests that intermolecular electron transfer is the predominant mechanism.
Abstract: The quenching of the luminescence of the uranyl ion by other metal ions has been studied in aqueous solution. The quenching is shown to be a dynamic process, and the correlation of the logarithm of the quenching rate with the metal ion ionization potential suggests that intermolecular electron transfer is the predominant mechanism. Evidence that this involves complete electron transfer comes from flash photolysis of solutions of UO2+2 and manganese(II), where a broad absorption (λmax= 505 nm) is observed which is assigned to Mn3+. Consideration of the energetics of the quenching process suggests that in the quenching of uranyl by silver(I), the products (UO+2 and Ag2+) are produced in their electronic ground states. Studies of the effect of temperature on the quenching suggest that if an intermediate complex (exciplex) is involved in the quenching then this must involve only very weak binding. With silver(I), the quenching is sensitive to the ionic strength of the solution. Further studies suggest that the lifetime of the luminescent state of the uranyl ion in aqueous solution varies with both temperature and uranyl ion concentration.
60 citations
TL;DR: In this paper, the rate constants in quenching reaction of uranyl luminescence by halide ions were determined from luminecence lifetime measurement, showing that an electron transfer process plays an important role in the quench of halide ion.
50 citations
TL;DR: In this paper, the excitation and emission transitions involved in the green luminescence of the octahedral UO 6-6 group in oxides with perovskite structure are reported and discussed.
43 citations
TL;DR: In this paper, the authors investigated the effects of photolysis of aqueous solutions of UO 2+2 and some inorganic anions formed by one-electron photo-oxidation by uranyl followed by reaction with the corresponding anion.
25 citations
TL;DR: The crystal structures of Cs2UO4, Cs4U5O17 and Cs 2U7O22 have been revealed by X-ray diffraction as discussed by the authors.
24 citations
TL;DR: Some uranyl complexes with hexamethylphosphoramide (HMPA) and urea were prepared and characterized in this paper, where the properties of UO 2 (NO 3 ) 2 ·2(HMPA).
23 citations
TL;DR: In this article, a study of photochemical reactions of uranyl ions in aqueous acid solutions was carried out by means of flash photolysis, where short-lived absorption (∼ 10 −4 s) was observed on flash excitation of UR in solution and was assigned to singlet-singlet transitions.
TL;DR: In this paper, a brief discussion is made on the ligation effect of nitrate group on the uranyl bond order from a point of view of molecular orbital theory, and a detailed analysis of the effect of the nitrate ion ligation on the UO2X3 − (X = NO3) ions belonging to a point group of D3h is given.
Abstract: Laser Raman spectra of uranyl trinitrate complexes (KUO2(NO3)3, RbUO2(NO3)3, CsUO2(NO3)3, NH4UO2(NO3)3) have been measured in the region from 2000 cm−1 to 10 cm−1. Vibrational assignments have been made on the assumption that all the complexes contain discrete UO2X3 − (X = NO3) ions belonging to a point group of D3h. A brief discussion is made on the ligation effect of nitrate group on the uranyl bond order from a point of view of molecular orbital theory.
TL;DR: In this article, the UO2LnX2, where L is di-2-pyridyl ketone, N = 2 (X = Cl, NCS, ClO4) or n = 1 (x = NO3), has been prepared and characterized by elemental analyses, molar conductivity and thermoanalytical measurements.
TL;DR: In this paper, a polymeric structure involving bridging oxygen atoms has been suggested on the basis of their thermal, IR, Raman and X-ray diffraction studies and other properties.
TL;DR: In this paper, the changes in free energy, enthalpy and entropy for the formation of uranyl(VI)-glycolate complexes, have been determined at 25 °C and in aqueous perchlorate medium 1.00 M.
TL;DR: In this article, the performance of ammonium uranyl vanadate has been investigated with roentgenographic and spectroscopic methods and the analysis of the powder diagramm shows that the compound is structurally related to the mineral Carnotite.
Abstract: Hydratisiertes Ammonium-Uranyl-Vanadat wurde rontgenographisch und schwingungsspektroskopisch untersucht Die Auswertung des Pulverdiagramms erwies, das die Substanz mit dem Mineral Carnotit strukturell verwandt ist Auch die IR- und Raman-Spektren bestatigten diese Verwandschaft Die thermische Zersetzung von NH4UO2VO4 · nH2O wurde erneut untersucht Das dabei gebildete Uranyldivanadat, (UO2)2V2O7, wurde eingehend charakterisiert und das Verhalten bei Temperaturen bis zu 1200°C untersucht
Ammonium Uranyl Vanadate and the Products of its Thermal Decomposition
Hydrated ammonium uranyl vanadate has been investigated with roentgenographic and spectroscopic methods The analysis of the powder diagramm shows that the compound is structurally related to the mineral Carnotite The i r and Raman spectra also confirm this relation The thermal behaviour of NH4UO2VO4 · nH2O is also reinvestigated and the uranyl divanadate, (UO2)2V2O7, produced during this decomposition is fully characterized Its behaviour in the temperature range up to 1200°C is also investigated
TL;DR: In this article, the reactions of the cyclic Schiff base derived from heptane-2,4,6-trione and ethylenediamine with uranyl(VI), copper(II), nickel(II) and cobalt (II) are reported.
Patent•
26 Jul 1976
TL;DR: A direct nuclear radiation pumped laser consisting essentially of a uranyl salt with a UO2 ++ uranyl ion enriched in the U235 isotope sufficient to sustain a fission chain reaction is described in this paper.
Abstract: A direct nuclear radiation pumped laser consisting essentially of a uranyl salt with a UO2 ++ uranyl ion enriched in the U235 isotope sufficient to sustain a fission chain reaction, the uranyl ion being directly nuclear radiation pumped by a fission power transient of the core to produce laser action between a low-lying vibrational level of the first triplet electronic state and an upper vibrational level of the singlet ground state.
TL;DR: In the presence of pyridine N-oxide (Opy), both monomeric and polymeric [UO2(oda)-(Opy)-n(n=∞) complexes were obtained as mentioned in this paper.
TL;DR: In this article, the properties of the cyclic polyethers dibenzo-18crown-6 and benzo-15crown5 have been characterized by elemental analyses, molar conductances, infrared and electronic spectra, and thermal analyses.
TL;DR: In this article, the infrared and laser-Raman spectra of synthetic carnotite, K2[(UO2)2V2O8], are reported and discussed.
Abstract: The infrared and laser-Raman spectra of synthetic carnotite, K2[(UO2)2V2O8], are reported and discussed. Force constants for the terminal V-O bonds as well as for the UO22+ ions are evaluated. From the spectroscopic data, a U-O bond length of 1.81 A is estimated for the uranyl ion in this compound.
TL;DR: In this paper, it was shown that the inequality in the bond lengths of the pairs C(13)-C(14), C(14-C(15) and C(15)-O(16), O(17) is not consistent with such a description.
Abstract: approximately parallel in adjacent molecules. The other phenyl ring has near-neighbour phenyl rings which are roughly perpendicular to it. Table 6 contains the shorter non-bonded contacts of O(16) and O(17). The outstanding feature is that O(16) has contacts with C(4), C(5) and C(6) of an adjacent molecule which are just greater than van der Waals contacts. Hence the environment in the vicinity of the hydrogen bond is asymmetric. This 1,3-diketone is symmetrically substituted in the 1and 3-positions. It might be expected that an equilibrium mixture of the two possible enol tautomers would result. The inequality in the bond lengths of the pairs C(13)-C(14), C(14)-C(15) and C(13)-O(16), C(15)-O(17) is not consistent with such a description. For a unique enol, the values of these bond lengths would be approximately 1.47, 1.33 and 1.2, 1.4/~. If the final atomic positions obtained represented an average of the two enol tautomers, and any other combinations which might arise due to packing in the crystal, large thermal motion would be expected along the bond directions. This was not evident before or after correction for rigid-body motion. Our evidence, therefore, suggests a unique enol form which has been distorted by an asymmetric environment.
TL;DR: In this article, the IR spectra show that in all the adducts both the ligands and the metal coordinate the metal through the carbonyl oxygen atom, and the uranyl complexes exhibit their most usual six-coordination around the central monodentate molecules of the organic ligand.
TL;DR: In this paper, the U(IV) species and benzil (1) as the main photoredox products, and small amounts of 4-hydroxy-4-phenylbutan-2-one (2), trans-4phenyl-3-buten-2, and an unidentified product (4) are formed in the absence of the uranyl ion.
Abstract: Irradiation of benzaldehyde in a deoxygenated aqueous acetone solution in the presence of the uranyl ion with light of λ≥365 nm gives the U(IV) species and benzil (1) as the main photoredox products, and small amounts of 4-hydroxy-4-phenylbutan-2-one (2), trans-4-phenyl-3-buten-2-one (3), and an unidentified product (4). None of them are formed in the absence of the uranyl ion. The products 2 and 3 are assumed to be formed by the uranyl ion-photocatalyzed condensation of benzaldehyde with acetone. Irradiation of acetophenone in the presence of the uranyl ion gives no photoproducts, though the uranyl emission is effectively quenched. p-Methoxybenzaldehyde and p-chlorobenzaldehyde give the corresponding 4,4′-disubstituted benzils respectively by irradiation under similar conditions. The quantum yield for the formation of the U(IV) species decreases whereas the quenching constant increases with the increase in the electron donating power of the substituent. The physical quenching process appears to compete s...
TL;DR: In this article, complexes of composition Th(NO3)4·3L (L = MeCONHEt [ea]), MNO34·2.5L (M=Th, L = Mecon(Pri)2 (dipa) and UO2NO3·2L(L = dipa) have been prepared and their IR, Raman and electronic spectra are reported.
Patent•
19 May 1976TL;DR: In this paper, a process for separation of uranium isotopes by chromatography through an anion exchange material is found to be improved in efficiency of separation as well as in productivity by addition of a catalyst for accelerating electron exchange reactions occurring in the system under conditions to retain uranyl ions on the anion exchanged material preferentially over uranous ions.
Abstract: A process for separation of uranium isotopes by chromatography through an anion exchange material is found to be improved in efficiency of separation as well as in productivity by addition of a catalyst for accelerating electron exchange reactions occurring in the system under conditions to retain uranyl ions on the anion exchange material preferentially over uranous ions.
Patent•
14 Sep 1976
TL;DR: In this article, a process for treating the aqueous effluents that are produced in converting gaseous UF6 (uranium hexafluoride) into solid UO2(uranium dioxide) by way of an intermediate (NH4)4 UO 2 (CO3) 3 ("AUC" Compound) is disclosed.
Abstract: A process for treating the aqueous effluents that are produced in converting gaseous UF6 (uranium hexafluoride) into solid UO2 (uranium dioxide) by way of an intermediate (NH4)4 UO2 (CO3) 3 ("AUC" Compound) is disclosed. These effluents, which contain large amounts of NH 4 (ammonium), CO3 (carbonate), F (fluoride), and a small amount of U (uranium), are mixed with H2SO4 (sulfuric acid) in order to expel CO2 (carbon dioxide) and thereby reduce the carbonate concentration. The uranium is precipitated through treatment with H2O2 (hydrogen peroxide) and the fluoride is easily recovered in the form of CaF2 (calcium fluoride) by contacting the process liquid with CaO (calcium oxide). The presence of SO4 (sulfate) in the process liquid during CaO contacting seems to prevent the development of a difficult-to-filter colloid. The process also provides for NH3 (ammonia) recovery and recycling. Liquids discharged from the process, moreover, are essentially free of environmental pollutants. The waste treatment products, i.e. CO2, NH3, and U are economically recovered and recycled back into the UF6->UO2 conversion process. The process, moreover, recovers the uranium as a precipitate in the second stage. This precipitate is a new inorganic chemical compound UO4.2NH3.2HF [uranyl peroxide-2-ammonia-2- (hydrogen fluoride)].
TL;DR: The enthalpies of dissolution of anhydrous and hydrated uranyl formates, formic acid and hexahydrated URanyl nitrate in nitric acid at different concentrations have been measured and the following enthalps of formation have been determined as discussed by the authors.