Actinides absorption spectra

The first attempts to record the Bk(IV) solution absorption spectrum were hindered by the presence of cerium impurities (92). The positions of the Bk(IV) absorption bands, superimposed on the strong Ce(IV) bands, suggested the assignment of Sf7 for the electronic configuration of Bk(IV), in agreement with the actinide hypothesis. 

The absorption spectrum of the hexagonal form of BkCls as a function of time. The changes in the spectrum are due to the formation of CfCF. Note the sharp Tanthanide-like transitions characteristic of the later actinide (-1-3) state, (from J.R. Peterson et al, Inorg. Chem., 1986, 25, 3779 reproduced by permission of the American Chemical Society). 

Akiyama et al. (2001) s)mthesized and isolated some light actinide metallofullerenes such as U C82, Np Cg2/ and Am C82 and foimd the valency of U atom in C82 cage is 3-I-, showing almost exactly the same UV-Vis-NIR absorption spectrum as that of the bivalent lanthanide C82 metallofullerenes such as La Cs2 and Gd C82-... 

The triacetate uranyl complex (24) is structurally similar to the trinitrate uranyl complex (6) (three bidentate ligands arranged equa-torially around the uranyl O—U—O axis). It was expected that the visible, near ultraviolet spectrum of the triacetate uranyl complex would be similar to the spectrum of U02(N03)3 as are the spectra of 1102(804)3, 1102(003)3 , and other uranyl complexes which apparently have the same structure (17). The absorption spectrum of uranyl acetate extracted into tri-n-octylamine in xylene from dilute acetic acid is different from the trinitrato uranyl spectrum. This indicates that the triacetate uranyl complex is probably not the species involved. By analogy to the uranyl nitrate system 14), formation of a tetraacetate uranyl complex might be expected. The purpose of this work is to determine the nature of the anionic hexavalent actinide acetate complexes and to identify the species involved in the amine extraction and anion exchange of the hexavalent actinides from acetate systems. 

Only two studies of transcurium-ion fluorescence in solution have been published. Carnall etal. (1984) measured the absorption spectrum of Bk ", interpreted its energy-level structure in terms of a free-ion energy-level model, analyzed its absorption band intensities in terms of Judd-Ofelt theory, and reported luminescence lifetime data for aquated Bk in DjO. Beitz et al. (1983) carried out LIF studies on Es " in HjO and DjO solutions as well as complexed Es " in an organic phase. No luminescence studies have been reported for actinide elements heavier than Es. 

The majority of the photochemical studies with actinide ions have been carried out with the uranyl (UC ion. This ion is yellow in color both in the solid and solution states. The early photochemistry of this ion has been reviewed. " Excitation of this ion results in an LMCT absorption that involves a transition from an essentially nonbonding 7r-orbital on oxygen into an empty 5/orbital on uranium. This LMCT assignment is that given to the weak visible bands in the absorption spectrum at 500 nm and 360 nm. The absorption spectrum also shows a series of bands of increasing intensity to higher energy. The positions of the absorption bands of are very sensitive to both temperature and the chemical environment... 

Absorption and Fluorescence Spectra. The absorption spectra of actinide and lanthanide ions in aqueous solution and in crystalline form contain narrow bands in the visible, near-ultraviolet, and near-infrared regions of the spectrum. 

Electronic absorption bands in the spectrum of PrCls (aq) reproduced with permission from S.A. Cotton, Lanthanides and Actinides, Macmillan (1991) p. 30. 

Absorption and Fluorescence Spectra. The absorption spectra of actinide and lanthanide ions in aqueous solution and in crystalline form contain narrow bands in the visible, near-ultraviolet, and near-infrared regions of the spectrum (13,14,17,24). Much evidence indicates that these bands arise from electronic transitions within the 4f and 5/shells in which the 4f and bf configurations are preserved in the upper and lower states for a particular ion. 

The absorption spectra of these complexes can be obtained in the visible and near infrared region using solutions of the triphenylphos-phonium salts, but if the ultraviolet spectrum is desired, the complex must be formed in solution using an aliphatic quaternary ammonium halide and the actinide trihalide or oxyhalide. 

For thorium there are only estimates of the corresponding potential. An early estimate, of -2.4 V, was based on a relation between this quantity and the frequency of the first electron transfer absorption band in the UV spectrum of an aqueous thorium perchlorate solution (9). However, the spectral measurements did not quite reach the absorption maximum, and the necessary extrapolation introduced some uncertainty. Another value, -3.6 V, was based on the RESPET treatment of J0rgensen (10,11). The adjustable parameters in the RESPET equation were fixed using experimental values for other actinide elements (12). This method yields a value of -0.69 V for U(IV)/(III). Another rather simple method correlates this potential with the number of 5/"electrons for the element and gives -3.41 V for thorium and -0.54 V for uranium (13). A more sophisticated estimate (14), using a method proposed by Nugent et al. (12) (described later), gave -3.8 V for thorium. 

The separation of trivalent actinides, such as and is of major concern in the field of nuclear technology. Den Auwer et al. (2000) studied the structure of N,N,N ,N -Tetraethylmalonamide (TEMA) complexes of lanthanides and americium by several methods including the X-ray absorption technique. They carried out first the X-ray diffraction study of the single crystals of Nd(N03)3(TEMA)2 and Yb(N03)3(TEMA)2 and compared the EXAFS spectra of these complexes in a solvent phase. The metal-centered polyhedron in the solvent phase was found to be similar to that of the solid-state complexes. They also measured an EXAFS spectrum of the Am(N03)3(TEMA)2 complex in the solvent phase and confirmed the similar coordination spheres with the Nd complex. 

The UV-Vis spectroscopy of lanthanide and actinide elements directly reflects the electronic structure of the species involved. In oxidation states (III) and (IV), the ground-state electronic configuration is/", thus the low-lying spectrum is dominated by/-/ transitions that are strictly parity forbidden, and can also be spin-forbidden although spin-orbit coupling attenuates the selection rules. Nevertheless, both restrictions have important consequences, namely that these /-/ bands have very low absorption intensities, and the radiative lifetimes of/-/ states are often rather large (10 s) and sensitive to the environment. This is routinely used in Time-Resolved-Laser-Fluoresence-Spectroscopy (TRLFS) of Eu(III) and Cm(lII) at approximately 17000 [49-51]. Metal-centered/-rf transitions occur... 

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