Nature of chemical bonding in ThF4

Abstract

The fine structure of the X-ray photoelectron spectrum of ThF4 in the range of valence electrons (binding energy from 0 to 35 eV) is examined. The analysis takes into account the results of theoretical calculation of the electronic structure of the ThF84− cluster (point group C2) as a model of the nearest surrounding of the Th atom in ThF4, performed by the relativistic discrete variation method. It is demonstrated theoretically and confirmed experimentally that formation of a chemical bond gives rise to filled states of Th5f electrons (∼0.5 Th5f electron) in the energy range of electrons of outer valence molecular orbitals (valence band). The Th6p electrons noticeably participate in formation not only of inner valence but also of outer valence (∼0.4 Th6p electron) molecular orbitals. The composition and order of inner valence molecular orbitals in the energy range from 13 to 35 eV is determined, and the density of states of valence electrons in the range from 0 to 35 eV in ThF4 is calculated. The results obtained allowed the fine structure of the high-resolution O4,5(Th)-emission spectrum of thorium in ThF4 in the photon energy range from ∼60 to ∼85 eV, associated with the formation of outer and inner valence molecular orbitals, to be interpreted for the first time.