Effective Actinide Ion Charges in AnO2 (An = Th‒Lr)

Abstract

The electronic structure of AnO₂ (An = Th‒Lr) and the structure of X-ray photoelectron spectra of their valence electrons were calculated by the relativistic discrete variation method in the MO LCAO cluster approximation (molecular orbitals as linear combinations of atomic orbitals). This structure is in satisfactory agreement with the available experimental spectra. The effective charges Q_An of the An ions in AnO₂ were determined as the difference between the number of electrons in the neutral An atom and the number of electrons in the actinide ion in the AnO₈ cluster. The dependence of the effective charges Q_An in AnO₂ on the atomic number Z was obtained. The estimated values in the range 0.42 e < Q_An < 1.04 e differ significantly from Q_An(IV) = 4 e, found in the ionic approximation. This is attributed to the significant covalence effects in AnO₂, associated with the overlap of not only An6d, but also of An6p and An5f AOs with the oxygen orbitals. There is qualitative agreement between the obtained Q_An values and the values of the chemical shifts (several electron-volts) of the lines of the actinide 4f core electrons in the XP spectra of dioxides relative to the metals.