5F core

Es, [Rn]ls 5f, core electron configuration corresponds to the noble gas radon. Besides that there are 2 electrons in the 75-orbital and 11 electrons in the 5/-orbitals. 

Trivalent americium oxides are expected to have a 5f core and therefore should display a zero moment. Due to the existence of low-lying excited electronic states, this zero moment is difficult to observe experimentally (Kannelakopulos et al. 1978). Measurements (Soderholm et al. 1986) of a pure A-type americium sesquioxide have indicated temperature-independent paramagnetism from 5 to 300 K. In other work, Karraker (1975a) studied Am02 between 2 and 97 K, but found two different regions that displayed Curie-Weiss behavior. 

The Mott-like transition, a central concept for the description of the actinide metal series, causes the sudden increase of the atomic volumes, encountered when between Pu and Am (Fig. 3). All other properties indicate the onset of a 5f localized behaviour at Am (see Part V) the 5 f pressure, which had contained to smaller values the equilibrium interactinide distance, suddenly gives in, with the withdrawal of the 5f s within the atomic core. The occurrence of such a transition within a series characterized by an unsaturated shell, is a unique phenomenon of the actinide series. In lanthanides, it does not occur except perhaps under pressure in cerium metal the approaching of cerium atoms induces suddenly the itineracy of 4f orbitals and a sudden volume collapse - see Chap. C. Neither it occurs in d-transition metal series, where the atomic volumes have an almost parabolic behaviour when plotted vs. Z (see Fig. 3 and Chap. C). The current... 

We have calculated the Radon core diamagnetism for actinide ions up to americium the results are reported in Table 6. These values are smaller than usually assumed in the literature. Diamagnetic contribution for localized 5f electrons are also given - From Table 6, we see that the core diamagnetism is large and has to be taken into account when a detailed analysis of the susceptibility is made. In the case of Th metal, for example, it amounts to 40% of the experimental susceptibility. 

The most important information (by Baer and Schoenes ) obtained when using the combined XPS/BIS method is the Coulomb interaction energy Uh that we have discussed in Part II. For UO2, Uh = 4.6 0.8 eV has been obtained. This large separation between the two final states (2(5f ) —> 5f + 5f ) is in itself a hint to the localized character of the 5 f states in UO2. Baer and Schoenes compared the value for Uh with theoretical values they found an agreement with Uh = 4 eV as calculated by Herbst et al. for a U" " metal core. As discussed in Chap. A, intraatomic calculations of Uh in metals possibly underestimate screening by conduction electrons nevertheless, they should be valid in the case of an insulating solid as UO2. 

If the 4f core level spectra of the sesquioxides are taken into account (Figs. 31, 32), an interpretation may be forwarded based on a comparison with the spectra of the metals. As we have seen in Part III, to the main 4 f line of Am metal a 6 d screening, and to its low binding energy satellite a 5f screening are attributed. For Pu metal, the main line is attributed on the contrary to 5 f screening (in consistence with the good itinerant... 

It is worthwhile to mention the ample use of screening final states models in understanding core levels as well as valence band spectra of the oxides. The two-hole models, for instance, which have been described here, are certainly of relevance. Interpretational difference exists, for instance, on the attribution of the 10 eV valence band peak (encountered in other actinide dioxides as well), whether due to the non-screened 5f final state, or to a 2p-type characteristics of the ligand, or simply to surface stoichiometry effects. Although resonance experiments seem to exclude the first interpretation, it remains a question as to what extent a resonance behaviour other than expected within an atomic picture is exhibited by a 5 f contribution in the valence band region, and to what extent a possible d contribution may modify it. In fact, it has been shown that, for less localized states (as, e.g., the 3d states in transition metals) the resonant enhancement of the response is less pronounced than expected. 

As already mentioned in Section 4, the 5 s and 5 p core level spectra of the 5f-series and a number of the preceding elements should show pronounced effects of giant Coster-Kronig fluctuation and decay processes much in the same way as happens in the 4.S, 4 p spectra in the range 48 Z < 70. In the case of the 5 p spectrum, the gCK interaction process becomes... 

The results of a preliminary study of a sample of berkelium oxide (Bk02, Bk203, or a mixture of the two) via X-ray photoelectron spectroscopy (XPS) included measured core- and valence-electron binding energies (162). The valence-band XPS spectrum, which was limited in resolution by photon broadening, was dominated by 5f-electron emission. 

The consequent increase in the nuclear charge and reduction of the shielding of the 6d- and 7s-electrons lead to a contraction of the atomic radius, similar to that previously discussed for the ionic radius. In Am and Cm, the 5f-electrons are localized in the core, which causes an expansion of the atomic radius. The differences in localization of f-electrons between light and heavy actinides are also illustrated by their different superconductive and magnetic behavior. The Th, Pa, and Am metals are superconductors Tc of 1.37, 0.42, and 0.79 K, respectively), whereas the heavier actinide metals are not superconductors but have larger magnetic moments at low temperatures. 

The n=l and 2 shells were frozen at the ground-state Hartree—Fock values. The orbital set included the 4s,3p,3d,4f and 5g natural orbitals and 3p,3d,4s,4p,4d,4f,5s,5p,5d,5f orbitals from frozen-core Hartree—Fock calculations to provide representations for states whose dominant configuration is 13s n/). This set was again augmented by extra ad hoc orbitals to increase flexibility. The full set contained 24 orbitals (6 s-type, 7 p-type, 6 d-type, 3 /-type, 2 g-type) which were all orthogonalised using the prescription for two orbitals a) and b)... 

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