Absorption Spectra of the Octahedral Complex AmBr63- in the Cs2NaLuBr6 Crystal

Absorption spectra of the Cs₂NaLuBr₆:Am³⁺ (5 mol % of ²⁴³Am) were studied in the 450-2500 nm range at temperatures from 300 to 15 K. The spectra exhibited transitions from the ground level ⁷ F ₀ of the Am3+ (f ⁶) ion to the levels belonging to the ground term (⁷ F ₂, ⁷ F ₄, and ⁷ F ₆) and to the levels of the three excited states: ⁵ L ₆, ⁵ G ₂, and ⁵ D ₂. The vibronic pattern analysis for these transitions enabled localization of 17 electronic sublevels of the americium ion in the octahedral complex AmBr₆ ^3-. One sublevel of the electronic level with odd J value (⁷ F ₅) was localized for which the transition from the ground ⁷ F0 level is forbidden in accordance with the Judd-Ofelt theory. The crystal-field paramaters of the complex studied were calculated.     

Composition and stability constants of Np(V) fluoride complexes in chloride-fluoride melts

The absorption spectra of the NpO₂⁺ ion in the region of the ³ H ₅← ³ H ₄ magnetic dipole transition (∼1650 nm) in chloride-fluoride melts based on the eutectics NaCl-KCl-CsCl, NaCl-CsCl, and RbCl-CsCl at 650–750°C were recorded. The equilibrium concentrations of neptunium fluoride complexes in these melts were determined from the relative intensities of the NpO₂⁺ absorption bands. Existence of the complexes [NpO₂Cl₃F]³⁻ and [NpO₂Cl₂F₂]³⁻ was established, and the step stability constants of these complexes in melts of various cationic compositions were calculated.     

First Observation of the Cation-Cation Interaction of Actinides in Melts: NpO2 +-UO2 2+ System

Study of the absorption spectra of the NpO ₂ ⁺ ion in a CsCl melt containing 2 M UO ₂ ²⁺ , as well as in K₂UO₂Cl₄ and Cs₂UO₂Cl₄ melts (T = 700°C), allowed the first detection of the cation-cation interaction of actinides in melts. In all the molten salts studied, the cation-cation interaction of NpO ₂ ⁺ and UO ₂ ²⁺ is manifested most clearly (via appearance of an additional band) in the ³ H ₅ ³ H ₄ magnetic-dipole transition of the 5f ² configuration of the NpO₂ ⁺ ion (D _4h symmetry) near 1.6 m: Along with a sharp peak of unbound neptunyl(V) at 1660 nm, there is an equally sharp peak at 1633 nm belonging to the cation-cation complex. The intensity ratio for the peaks at 1633 and 1660 nm increases in the series of melts (UO ₂ ²⁺ in CsCl) < K₂UO₂Cl₄ < Cs₂UO₂Cl₄ by two orders of magnitude.     

Absorption Spectra of Cs2NaNdBr6 Crystal

The electronic and IR absorption spectra of the Cs₂NaNdBr₆ crystal were measured for the first time. By vibronic pattern analysis were localized 32 electronic transitions in the absorption spectra of the octahedral complex NdBr₆ ^3-. Combined analysis of the spectra of neodymium hexachloro and hexabromo complexes provided in a number of complex cases more precise localization of the electronic sublevels of both NdBr₆ ^{3 -} and NdCl₆ ^3-. The crystal-field (CF) parameters were calculated for the Cs₂NaNdBr₆ crystal. It was shown that the CF parameters for the NdBr₆ ^3- complex are by ca. 15% smaller than those for NdCl₆ ^3-.     

Formation-decomposition equilibrium of the NpO<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>·UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> complex in chloride melts

The absorption spectra of the NpO ₂ ⁺ (5f ²) ion were examined in the region of the 3H ₅ ← ³ H ₄ magnetic dipole transition (1530–1760 nm) for series of melts with the UO ₂ ²⁺ concentration varied in the opposite directions: (1) NaCl-2CsCl eutectic melt with growing additions of the Cs₂UO₂Cl₄ complex salt and (2) Cs₂UO₂Cl₄ melt with growing additions of the NaCl-2CsCl mixture. Measurements of the integrated intensities of the bands belonging to the NpO ₂ ⁺ ·UO ₂ ²⁺ complex and unbound NpO ₂ ⁺ throughout the UO ₂ ²⁺ concentration range examined (up to 4.4 M in neat Cs₂UO₂Cl₄ melt) and processing of the data obtained in terms of the mass action law showed that the formation-decomposition reaction of the cation-cation complex can be described adequately only using the equation of reaction in the form NpO₂Cl ₄ ^3? + UO₂Cl ₄ ^2? ? {Cl₄ONpO?UO₂Cl₃}^4? = Cl^? (with the equilibrium constant of 1.3±0.1). Thus, the formation of the cationcation complex should be treated as replacement of chloride ion in the equatorial plane of uranyl(VI) by neptunyl(V), rather than as simple addition of UO ₂ ²⁺ to NpO ₂ ⁺ . The reverse reaction, decomposition of the cation-cation complex, consists essentially in replacement of neptunyl(V) by chloride ion.     

NpO 2 + -UO 2 2+ cation-cation interaction in NaCl-KCl-CsCl and LiCl-KCl-CsCl eutectic melts

Absorption spectra of the NpO ₂ ⁺ ion in UO ₂ ²⁺ -containing NaCl-KCl-CsCl (0.300:0.245:0.455) and LiCl-KCl-CsCl (0.575:0.165:0.260) eutectic melts in the region of the 5f-5f transitions, 700–2000 nm, were studied at 650 and 500°C, respectively. Processing of the spectra allowed the previously discovered phenomenon, cation-cation interaction of actinides in melts, to be interpreted for the first time in terms of the mass action law. It was shown that, at the concentrations of the interacting components studied (C _Np = 0.2 M and C _U = 0.1–2 M), a 1: 1 NpO ₂ ⁺ ·UO ₂ ²⁺ cation-cation complex is formed. Its concentration stability constant was estimated at 0.06(6) and 0.11 1 mol^?1 for the NaCl-KCl-CsCl and LiCl-KCl-CsCl systems, respectively.     

Initiation of luminol chemiluminescence by two-quantum excitation of U(IV) in aqueous solution

Results of experiments on initiation of luminol chemiluminescence by multiquantum excitation of U(IV) in aqueous solution by dye laser radiation in the visible range are reported.     

Luminescence Spectra of Am3+ in Cs2NaLuBr6:Am3+ Bromoelpasolite

Luminescence spectra of the cubic crystal of Cs₂NaLuBr₆:Am³⁺ (2.5 mol % ²⁴³Am) were studied in the region of the (² G ₂, ⁵ D ₂) ⁷ F ₀ (460-490 nm) and ⁵ L ₆ ⁷ F ₀ (510-540 nm) transitions in the range from room temperature to 12 K. From the analysis of the vibronic pattern of the spectra, the zero-phonon 0-0 transitions forbidden for the O _h symmetry were localized, and the first data on the splitting sublevels of the actinide element (Am³⁺, 5f ⁶) in the field of the ideal octahedron of the AmBr₆ ^3- type were obtained. It was found that in the wavelength ranges indicated, the crystal studied exhibits a fairly strong self-luminescence due to the -decay energy of ²⁴³Am.