Trivalent actinides energy levels

An examination of the trivalent actinide energy level schemes reveals several possibilities for laser action. These are discussed in light of the general properties cited above. Only conventional broadband optical pump sources are considered. Obviously with selective laser excitation and cascade lasing schemes, stimulated emission from many more states should be possible, but these special situations are too numerous to be considered in detail here. 

In what follows we briefly review some of the previous attempts to analyze the available spectra of plutonium (6). In addition, we estimate energy level parameters that identify at least the gross features characteristic of the spectra of plutonium in various valence states in the lower energy range where in most cases, several isolated absorption bands can be discerned. The method used was based on our interpretation of trivalent actinide and lanthanide spectra, and the generalized model referred to earlier in the discussion of free-ion spectra. 

Electronic Energy Level and Intensity Correlations in the Spectra of the Trivalent Actinide Aquo Ions. I. Es3+, W.T. Camall, D. Cohen, P.R. Fields, R.K. Sjoblom, and R.F. Bames, J. Chem. Phys. 59, 1785-1789 (1973). 

We have calculated sets of theoretical energy levels for the trivalent actinides and lanthanides and correlated these levels with transitions observed in the solution absorption spectra of these elements. Using the eigenvectors resulting from this energy level calculation, we have computed the theoretical matrix elements required to account for the observed band intensities in the two series of elements. The extent to which the theoretical calculations can be correlated with experimental results has been discussed, and some applications for the intensity relationships are pointed out. 

Most published work on the energy levels in the trivalent lanthanides and actinides has been carried out in crystalline media, where the identity of a level in terms of a given coupling scheme can be experimentally established 8, 19). In attempting similar correlations in aqueous solution, one must rely heavily on the level identifications established in crystals. Where crystal data is not available, extrapolation of parameters... 

The same type of approach in terms of fitting energy levels to the absorption bands observed in the trivalent actinide elements has already been reported (4). Here the problems were somewhat more formidable because of the paucity of crystal data and the much greater density of levels observed in the spectral region over which solution absorption spectra could be obtained. Experimental data and calculated energy... 

The values of F2 for the trivalent lanthanides and actinides are plotted vs. Z (atomic number) in Figure 7, and those of f are shown graphically in Figure 8. Values of F2 and 5/ for actinides above curium were extrapolated from the light half of the series assuming a linear relationship for the parameters (9). These parameters, in turn, were used to calculate the expected energy levels for Es ", and Fm-" ". ... 

Table I. Parameters Used to Calculate Energy Levels Observed in the Solution Absorption Spectra of the Trivalent Actinides and Lanthanides...

Figure 7. Energy levels of trivalent actinide ions (----------predicted levels ...

The f-electrons of Am, though quite localized, are still very close to the Fermi level (like Ce) compared to most rare-earths, and the energy bandwidth is comparable to that for Ce. Therefore, we should still expect some complexities in bonding and valence-level interactions. The entropy position of Am in Fig. 4 is representative of a rather normal trivalent metal exhibiting an "actinide-contraction" beginning at Ac. 

Brewer [12] has tabulated the energies of the low-lying configurations of the free ions of the trivalent lanthanides and actinides. The energies of the lowest levels of various configurations with respect to the f configuration, as a function of atomic number. 

Figure 4. Energies of the lowest levels of various configurations of the trivalent lanthanides and actinides (Ref. 12). 

Johansson (1978) and Brooks etal. (1984) utilized the energy difference (f d transitions) between trivalent (f"ds ) and tetravalent (f" M s ) cerium and other f-element metals to estimate thermochemical data for compounds. A similar approach has been used by Mikheev et al. (1986) and Spitsyn et al. (1985) to include the divalent as well as the tetravalent state. Again, a critical issue has been the behavior of the heavy actinides with respect to f- d transitions, and the need to utilize and to interpret the few experimental measurements on these actinides, which are discussed below (e.g., section 2.4.1.3). Johansson and Munck (1984) defined a function P (M) that removes the intershell multiplet coupling energy from the atomic reference state (A ,.,up,i j is the energy difference between the baricenter and the lowest level of a multiplet). For the lanthanides P (M) is significantly smoother than P(M),-except for an anomaly at Yb that may be due to an error in experimental data. Unfortunately, Johansson and Munck (1984) point out that spectroscopic data on the heavy actinides are inadequate to correct P(M) to P (M) for the actinides. 

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