We have calculated the onehyphen;electron energy level structures of the isolated species UO2++, UO2+, and UO2in their linear forms, using a selfhyphen;consistent relativistic multiple scattering model withXagr; exchange. For UO2++, we have used the molecular orbitals of the ground state muffinhyphen;tin potential to calculate the energies of a few of the manyhyphen;electron excited states; these afford a somewhat more fundamental basis for comparison with experiment than do the onehyphen;electron energies, and their determination also sheds some light on the coupling scheme (ohgr;ndash;ohgr; vs Lgr;ndash;Sgr;) to be expected in these systems. These excited state energies agree well with the experimental absorption data. The calculated onehyphen;electron excitation energies for UO2++are in reasonable agreement with the observed onset of absorption. The behavior of the corresponding onehyphen;electron binding energies as a function of Undash;O distance supports a different interpretation of the XPS than that given by Vealetal. Considering the three species at a common bond distance of 2.0 Aring;, we find that each contains roughly three 5felectrons; UO2++has three bonding 5fthinsp;rsquo;s, UO2+has two bonding 5fthinsp;rsquo;s and one nonbonding (localized) 5f, and UO2has one bonding 5fand two nonbonding 5fthinsp;rsquo;s. This agrees with XPS which exhibits two localizedfelectrons in UO2and none in UO2++.
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