Theoretical study of the4plevel photoemission spectra of Ba metal and related systems

Abstract

The $4p$ hole spectral function of Ba metal is calculated by an ab initio atomic Green's-function method. The atom-metal energy shifts of the interacting hole (particle) states are taken into account. It is shown that for a consistent description of the spectral line positions, intensities, and linewidths, it is necessary to take into account explicitly such energy shifts. The $4p$ x-ray photoelectron spectroscopy spectra of Ba metal and compounds are analyzed in detail. The $2s\ensuremath{-}4p$ x-ray emission spectroscopy spectrum of La metal is also discussed. For the $4p$ level ionization of Ba metal and compounds, the one-electron approximation breaks down. This is due to the Coster-Kronig (CK) ${4p\ensuremath{-}4d}^{\ensuremath{-}2}4f$ process by which an empty $4f$ level is filled by a $4d$ electron rather than by a ligand valence electron [charge-transfer (CT) screening] or a conduction-band electron. A possibility of suppression of both CK and CT core-hole screening in a final state by decay of a resonantly excited core-hole state and a fully relaxed core-hole state where an $4f$ empty level is already occupied in an initial core-hole state is discussed.