Actinide series electronic systems

This analysis is valid along the proposed actinide series. Accordingly, combining the 20 electrons from the Si2o cage, the 7s, 7p, 6d, and 5f electrons from the actinide plus the charge of the cluster, give the required electrons to form the 16 MOs of a centered 32-electron system (quoted by Piehon [46]). 

Manna D, Ghanty TK. Prediction of a New Series of Thermodynamically Stable Actinide Encapsnlated Fnllerene Systems Fulfilling the 32-Electron Principle. J Phys Chem C. 2012 116(48) 25630-25641. 

The occurrence of a heavy-electron state in metals is most distinctly observed in compounds where one of the chemical constituents is an element of the rare-earth (4f) or actinide (5f) series. Within these series, it is the elements at the beginning or the end of the res-Sective row of the periodic system that are most likely involved in this effect (Ce, Yb, U, Np). 

The actinide element series, like the lanthanide series, is characterized by the filling of an f-electron shell. The chemical and physical properties, however, are quite different between these two series of f-electron elements, especially in the first half of the series. The differences are mainly due to the different radial extension of the 4f- and 5f-electron wavefunctions. For the rare-earth ions, even in metallic systems, the 4f electrons are spatially well localized near the ion sites. Photoemission spectra of the f electrons in lanthanide elements and compounds always show "final state multiplet" structure (3), spectra that result from partially filled shells of localized electrons. In contrast, the 5f electrons are not so well localized. They experience a smaller coulomb correlation interaction than the 4f electrons in the rare earths and stronger hybridization with the 6d- and 7s-derived conduction bands. The 5f s thus... 

Discussing the transport properties of their compounds, it seems to be natural to start with the rare earth and actinide elements, which are all metals. As a matter of fact, pure metals are not always the simplest solid-state systems this is particularly true in the case of the transition-metal series, where d electrons may act as scattering centres and/or charge carriers. 

The role of the crystal-field interaction remain obscure in all these systems, both for actinides and cerium. Whereas in the other lanthanide NaCl-type compounds, LnX and LnZ, the easy directions are given by straightforward crystal-field considerations and the value of the crystal-field potential varies in a systematic way across the lanthanide series, this is not the case in the materials discussed here. The crystal-field energy levels can be measured in the cerium compounds with neutron inelastic scattering, but have not been observed in the uranium (or higher) actinides. It is assumed that this inability to observe directly the crystal-field levels is because they are strongly broadened by the interaction between the 5f and conduction electrons. This has been the subject of much work by Cooper and his collaborators. 

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