Resonances in 3dElectron Photoemission Predicted at Ni 2pThreshold for NiCl2and NiO

We report the calculation of the 3 d X-ray photoemission spectra (3 d XPS) in NiCl 2 and NiO at the Ni 2 p threshold photon energies, on the basis of a cluster model taking into account the intraatomic multipole electron-electron interactions. By utilizing much stronger resonances and rich structures at the Ni 2 p threshold compared with the 3 p threshold of the second-order processes 3 d n +ω→ p 5 3 d n +1 →3 d n -1 + ε with n =8 and 9, we show that the spectrum can give conclusive information about the 3d configuration of the initial and final states in these systems.