Relativistic electronic structure of UO2++, UO2+, and UO2

Abstract

We have calculated the one‐electron energy level structures of the isolated species UO₂⁺⁺, UO₂⁺, and UO₂ in their linear forms, using a self‐consistent relativistic multiple scattering model with Xα exchange. For UO₂⁺⁺, we have used the molecular orbitals of the ground state muffin‐tin potential to calculate the energies of a few of the many‐electron excited states; these afford a somewhat more fundamental basis for comparison with experiment than do the one‐electron energies, and their determination also sheds some light on the coupling scheme (ω–ω vs Λ–Σ) to be expected in these systems. These excited state energies agree well with the experimental absorption data. The calculated one‐electron excitation energies for UO₂⁺⁺ are in reasonable agreement with the observed onset of absorption. The behavior of the corresponding one‐electron binding energies as a function of U–O distance supports a different interpretation of the XPS than that given by Veal et al. Considering the three species at a common bond distance of 2.0 Å, we find that each contains roughly three 5f electrons; UO₂⁺⁺ has three bonding 5f ’s, UO₂⁺ has two bonding 5f ’s and one nonbonding (localized) 5f, and UO₂ has one bonding 5f and two nonbonding 5f ’s. This agrees with XPS which exhibits two localized f electrons in UO₂ and none in UO₂⁺⁺.