Many-body calculations of the core hole spectra of NiCO

Abstract

We performed the ab-initio 2h1p and 2h–2p/3h2p CI calculations of core hole spectra of NiCO using an extended basis set. The main line/satellite line energy separations and intensity ratios of the new high-resolution XPS core hole spectra of the CO/Ni system which other theoretical molecular approaches fail to predict correctly are well reproduced by the present 3h2p CI calculations. The present interpretation of the core hole spectra substantially differs from others because of neglect of the important many-electron effects in the lower satellite energy region by other molecular approaches. The lowest-energy state is the 1h state closer to the Koopmans state, not the 2h1p CT (charge transfer) shakedown state. The 2.1 eV carbon satellite is the π metal-ligand CT shakeup satellite (with respect to the 1h main line state). The intensity of the oxygen satellite is very small, in accord with experiment. The interpretation and the existence of this satellite is supported by the similarity of the 1s to 2π* resonance energy and the satellite energy. The 5.5 eV satellites are the σ CT shakeup states (with respect to the 1h main line state) rather than the Koopmans states or 2π to Rydberg levels. The importance of the relaxation effect of the σ bonding orbital is emphasized. The 8.5 eV oxygen and 9 eV carbon satellites are assigned as the ? CT shakeup excitations (2π* and to the higher Rydberg levels) rather than 1π to 2π* intraligand excitation.