Free-ion energy level structure for

The wave functions used in the expressions for the line strengths are precisely those deduced by an analysis of the free-ion energy level structure. Therefore, only three new parameters, the s, have been introduced to account for the line strengths. This scheme has been remarkably successful in modeling experimental observations in both crystal and solution environments. It also accommodates the existence of the "hypersensitive" transitions. Peacock (30) has recently reviewed the field with regard to lanthanide f-f transitions. The simplicity of this scheme has been utilized by Krupke (31) and Caird (32) to predict potential laser transitions in the lanthanides. 

Fig. 16.15 Absorption spectra of the quadrivalent actinide ions. Aquo-ion spectra are indicated for U, Np, and Pu, while the spectra of Am, Cm, and Bk are of solid AnF samples [112]. Estimated free-ion energy level structure is shown for first few excited states. See discussion in Section 16.4.3.)...

Prediction of the energy level structure for Pu2+ (5f ) is of particular interest since no spectra for this valence state of Pu have been reported. On the basis of what is known of the spectra of Am2+ (26), Cf2" (27), and Es2+ (28), there appears to be evidence for a very small crystal-field splitting of the free-ion levels. Such evidence encourages use of a free-ion calculation in this particular case. The parameter values selected are indicated in Table V. Based on the systematics given by Brewer (19), the first f- d transition should occur near 11000 cm-, so the f- -f transitions at higher energies would be expected to be at least partially obscured. A... 

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 electrostatic and spin-orbit parameters for Pu + which we have deduced are similar to those proposed by Conway some years ago (32). However, inclusion of the crystal-field interaction in the computation of the energy level structure, which was not done earlier, significantly modifies previous predictions. As an approximation, we have chosen to use the crystal-field parameters derived for CS2UCI6 (33), Table VII, which together with the free-ion parameters lead to the prediction of a distinct group of levels near 1100 cm-. Of course a weaker field would lead to crystal-field levels intermediate between 0 and 1000 cm-1. Similar model calculations have been indicated in Fig. 8 for Nplt+, Pu1 "1 and Amlt+ compared to the solution spectra of the ions. For Am t+ the reference is Am4" in 15 M NHhF solution (34). 

Figure 4.12 Schematic energy-level scheme for Ti sapphire laser material, highlighting the splitting of the 3d electronic state of the free Ti ion in the sapphire crystal field and the full vibronic level structure for Ti + - -sapphire. The main pumping and laser transition wavelengths are indicated.

The assumption of a large crystal-field interaction for Pu5+ spectra makes it necessary to conclude that while certain aspects of earlier free-ion estimates (37) are valid, the "assignment" of free-ion states to observed absorption bands was premature. Much of the structure must be due to crystal-field components of many free-ion groups that overlap in energy or to vibronic satellites similar to those encountered in CS2UCI6 (33). Thus, while the present computations would agree with earlier work in interpreting the levels observed in... 

We intend in this chapter to consider the manner in which the symmetry of the chemical surroundings of an ion determines the effect of this environment on the energy levels of the ion. In the crystal field and ligand field theories we often wish to regard the effect of the environment as a small perturbation on the states of the free ion. For the benefit of readers not acquainted with certain general features of the electronic structures of free atoms and ions, a brief resume of the subject is given in this section. 

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