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

On the basis of the fine X-ray photoelectron (0-similar to 1000 eV) and X-r ay emission (0-similar to 50 eV) spectral structure parameters as well as r esults of theoretical calculations of the electronic structure of UO2F2, th e study of the U6p,5f electronic states in this compound was done. As a res ult 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 si gnificant intensity of valence bands (0-similar to 15 eV) in X-ray photoele ctron spectra (XPS) of the outer valence molecular orbitals (OVMO) and rela tively intense peaks (similar to 96 and similar to 103 eV U5d <-- U5f trans itions) in X-ray O-4,O-5(U) emission spectra from UO2F2. Theoretical data a lso indicated the possibility of participation of the U5f atomic orbitals i n formation of the inner valence molecular orbitals (IVMO) (15-similar to 5 0 eV binding energy) formed mostly from the U6p and O(F)2s electrons of nei ghboring uranium and ligands O(F). On the basis of the X-ray O-4,O-5(U) emi ssion spectral structure parameters, the phenomenon of effective formation of such IVMOs first discovered on the basis of the XPS fine structure param eters was confirmed. (C) 2001 Elsevier Science B.V. All rights reserved.