Lanthanides spectra

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. 

Contents Analogies and Differences Between Monatomic Entities and Condensed Matter. -Rare-Earth Lasers. - Chemical Bonding and Lanthanide Spectra. - Energy Transfer. - Applications and Suggestions. 

The study of coordination compounds of the lanthanides dates in any practical sense from around 1950, the period when ion-exchange methods were successfully applied to the problem of the separation of the individual lanthanides,131-133 a problem which had existed since 1794 when J. Gadolin prepared mixed rare earths from gadolinite, a lanthanide iron beryllium silicate. Until 1950, separation of the pure lanthanides had depended on tedious and inefficient multiple crystallizations or precipitations, which effectively prevented research on the chemical properties of the individual elements through lack of availability. However, well before 1950, many principal features of lanthanide chemistry were clearly recognized, such as the predominant trivalent state with some examples of divalency and tetravalency, ready formation of hydrated ions and their oxy salts, formation of complex halides,134 and the line-like nature of lanthanide spectra.135... 

This volume of the Handbook on the Physics and Chemistry of Rare Earth begins with a Dedication to late Professor William (Bill) T. Camall who pioneered the interpretation of lanthanide spectra in solutions in the 1960s and 1970s. The Dedication is written by Drs. James V. Beitz and Guokui Liu from Argonne National Laboratory where Bill Camall spent his entire 37-year scientific career. 

Magnetic Dipole Transitions as Standards for Judd-Ofelt Parameterization in Lanthanide Spectra, C. Gorller-Walrand, L. Fluyt, A. Ceulemans, and W.T. Camall, J Chem. Phys. 95, 3099-3106 (1991). 

As the number of /-electrons increases, the process of assigning levels becomes more complicated. It is not often that the published results for lanthanide spectra in crystal media compare as favorably as those for... 

It is clear that the present results are consistent with the mechanism and formulation proposed by Judd. Of the three parameters t2, t4, and tq, it has been demonstrated that t2 has particularly interesting properties. Studies of lanthanide spectra in molten nitrate salts (2), in organic solvents (2, 16), and in the vapor phase 10, 11) have shown that the value of t2 can vary an order of magnitude or more depending upon the environment. Where it has been feasible to determine the values of 74 and T6 in systems where t2 was enhanced, it was found that they were nearly equal to those in aqueous solution. 

I am indebted to Jean Blaise for supplying data for the lanthanide spectra, and to Earl F. Worden, Jr., for the Cm separation. 

We do not attempt to give a full review of crystal-field theory, although we do include a substantial discussion that is perhaps somewhat lengthy. We believe that this is warranted from the point of view of the unique role that crystal-field theory has in the interpretation of lanthanide spectra. Numerous questions in this field still remain unanswered, and many of the major contributors over the years are stUl quite active, indicating that this area of research is mature but by no means exhausted. It is hoped that, by providing an extensive compendium of experimental data on lanthanide-ion spectroscopy, we will provide a further incentive for theoretical advances. 

Symmetry considerations have a profound effect on the interpretation of lanthanide spectra. We have already mentioned the effect of symmetry on selection rules for electric and magnetic dipole transitions and on the classification of crystal-field split energy levels. In this section, we consider the effect of symmetry on the crystal-field Hamiltonian itself. 

With the accuracy of the energy matrices assured, further advances in the analysis of complex lanthanide spectra could be carried out. The histories of the individual ions, complete up to a specified date (usually in 1976 or 1977), have been given by Martin et al. (1978). After 1978, many fits to lanthanide levels were carried out as a preliminary to other projects, such as the analysis of hyperfine structures or Rydberg series. This work is discussed in sections 8.4 and 8.5. Among articles in the classic vein that have not yet been mentioned are that of Wyart et al. (1976/7) on 4f and 4f °(5d-I-6s-I-6p) of Ho III, and that of Kaufman and Sugar (1978) on LuV 4f (5d -I- 6s -I- 6p). The Ndll analyses carried out by Blaise et al. (1984), which have been signposted in section 1, are other examples of that kind. 

The interpretation of the lanthanide spectra was further enhanced through the simultaneous developments of new experimental methods and instrumentation on the one hand, and the introduction of electronic computers for the performance of complex calculations, on the other hand. 

This chapter comprises two parts. In part 1 the theoretical methods for the energy-level calculations are discussed. Part 2 deals with the energy-level structure of the lanthanide spectra, as affected by their electronic properties and the strengths of the various interactions. The results and conclusions are obtained mainly through the use of the semiempirical method results of ab initio calculations are sometimes given for comparison. 

The Grotrian diagram of Prill 4f is given in fig. 1.4. This is one of the exceptional cases in the lanthanide spectra where a 4f configuration is almost completely known. 

PART 2. PROPERTIES AND METHODS OF INTERPRETATION OF THE LANTHANIDE SPECTRA... 

The lanthanide spectra, especially in low ionizations, are characterized by a high abundance of spectral lines and a high density of energy levels, both even and odd, in which no apparent regularity, such as a multiple structure, may be discerned. Consequently, these spectra are classified as very complex , and their successful interpretation has only recently been accomplished. 

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