Electronic Structures of Actinide Dioxides

The dependence of valence molecular orbital (MO) energies is obtained for AnO₂ (An = Th–Lr). The energies are calculated by the relativistic discrete variation (RDV) method depending on atomic number Z. Depending on the characteristics of the complex structures of theoretical and available experimental X-ray photoelectron spectra (XPS) of valence electrons in the binding energy range from 0 eV to ~50 eV, the features of the AnO₂ electronic structures are analyzed. This structure appears in the XPS spectra mainly due to the formation of both outer valence MOs from 0 eV to ~15 eV and inner valence MOs (IVMO) from ~15 eV to ~50 eV. The IVMO formation efficiency (experimental observation) characterizes the chemical bond features of actinide dioxides. Good agreement is reached between the calculated and available experimental XPS spectra of valence electrons. It allows us to understand the features of the chemical bond nature and the structures of XPS spectra of valence electrons in the AnO₂ series. Significant covalence effects are observed in AnO₂, which are caused by overlapping with ligand orbitals of not only An 6d but also 6p and 5f atomic orbitals.