Observation of dd excitations in NiO and NiCl2 using K-edge resonant inelastic x-ray scattering

The presence of dd excitations in K-edge resonant inelastic x-ray scattering in the 1s -> 4p region of transition-metal compounds and their excitation mechanism is established through measurements of NiO and NiCl2. It is demonstrated that the valence excitations are due to the interaction between the excited 4p electron and the 3d valence electrons. A detailed analytical framework for interpreting these excitations in transition-metal compounds is presented, demonstrating a strong angular dependence for different dd excitations.