Many-body effects in the4fx-ray photoelectron spectroscopy of theU5+andU4+free ions

Abstract

A strictly ab initio many-electron theory was used to calculate the $4f$ x-ray photoelectron spectroscopy (XPS) of the free ${\mathrm{U}}^{5+}$ and ${\mathrm{U}}^{4+}$ ions. The calculations, based on relativistic Dirac-Fock self-consistent field (DF-SCF) and Dirac configuration interaction (DCI) wave functions (WF's), indicate that the atomic spectra have a considerable multiplet structure. However, the multiplet splitting, which is mainly manifest as a broadening of the $4{\mathrm{f}}_{5∕2}$ and $4{\mathrm{f}}_{7∕2}$ lines, is not as strong as for the first-row transition metals. As expected, the ${\mathrm{U}}^{4+}$ primary peaks are broader and have more associated satellite structure than does ${\mathrm{U}}^{5+}$. A comparison of a synthetic spectrum for ${\mathrm{U}}^{4+}$ with the observed XPS of $\mathrm{U}{\mathrm{O}}_{2}$ indicates that interatomic, solid-state, effects may decrease the multiplet and spin-orbital splitting, relative to the free ion. Notably, the $7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ satellite characteristic of $\mathrm{U}{\mathrm{O}}_{2}$ is absent from the calculated XPS of ${\mathrm{U}}^{4+}$.