Charge transfer satellites and multiplet splitting in X-ray photoemission spectra of late transition metal halides

Core-level X-ray photoemission spectra (XPS) are calculated for Ni and Co dihalides with an MX₆ cluster model (M = Ni, Co; X = F, Cl, Br), where intra-atomic multiplet coupling as well as covalency mixing is taken into account. The effects of the intra-atomic configuration interaction between (3s)¹(3p)⁶(3d)ⁿ and (3s)²(3p)⁴(3d)ⁿ⁺¹, which is known to be important in the 3s XPS, are treated phenomenologically. The overall spectral shape of the Ni (Co) 2p XPS can be explained by a charge transfer mechanism, and the difference in the line shape between the Ni (Co) 2p _{3 2} and 2p _{1 2} XPS spectra is shown to originate from the multiplet splitting of their charge transfer satellites. However, the Ni (Co) 3s XPS are so complex that it is difficult to discriminate between exchange split pairs and their charge transfer satellites. As for Co dihalides, the spectral splitting of the 3s XPS mostly represents the 3s-3d exchange splitting of the (3s)¹(3d)⁸ configuration. However, in Ni dihalides the first satellite peak is mainly due to charge transfer.