The role of the U6p,5f electrons in chemical bonding of uranyl and uranium fluorides: X-ray photoelectron and X-ray emission studies

Abstract

Abstract On the basis of the fine X-ray photoelectron (0–∼1000 eV) and X-ray emission (0–∼50 eV) spectral structure parameters as well as results of theoretical calculations of the electronic structure of UO2F2, the study of the U6p,5f electronic states in this compound was done. As a result the U5f atomic orbitals (AO) were established to be able to participate directly in formation of molecular orbitals (MO) in UO2F2. In the MO LCAO approximation it allowed suggestion that in UO2F2 the filled U5f electronic states could exist. This was suggested to be one of the main reasons of significant intensity of valence bands (0–∼15 eV) in X-ray photoelectron spectra (XPS) of the outer valence molecular orbitals (OVMO) and relatively intense peaks (∼96 and ∼103 eV U5d←U5f transitions) in X-ray O4,5(U) emission spectra from UO2F2. Theoretical data also indicated the possibility of participation of the U5f atomic orbitals in formation of the inner valence molecular orbitals (IVMO) (15–∼50 eV binding energy) formed mostly from the U6p and O(F)2s electrons of neighboring uranium and ligands O(F). On the basis of the X-ray O4,5(U) emission spectral structure parameters, the phenomenon of effective formation of such IVMOs first discovered on the basis of the XPS fine structure parameters was confirmed.