Multiple-scattering approach to near-edge X-ray absorption fine structure of CO/NiO(100) and NO/NiO(100)

The carbon and nitrogen 1s near-edge X-ray absorption fine structure (NEXAFS) of CO/NiO(100) and NO/NiO(100) were calculated by the multiple-scattering cluster (MSC) method. The calculation shows that the shape resonance in C 1s NEXAFS spectra is attributed to the photoelectron scattered between the carbon atom and the substrate, and the weak features near the pi-resonance are caused by the shake-up effect. R-factor calculation demonstrates for the first time that the CO molecule is adsorbed at the asymmetric bridge site of the NiO(100) surface; the adsorption height of the carbon atom in the CO molecule is equal to 0.31 +/- 0.01 nm. Our MSC calculation supports former ab initio studies and the experimental results, i.e., CO/NiO(100) is a physisorption system, while NO/NiO(100) is a weak chemisorption system.