Resonant Soft X-Ray Emission Spectroscopy of NiO across the Ni L_2,3 Thresholds

We study the electronic structure of NiO using resonant soft X-ray emission spectroscopy across the Ni L_2,3 thresholds. We observe inelastic (Raman) features within 10eV of the elastic peak energy. At the L₃ resonance, the features within 4eV are enhanced and can be directly assigned to the d-d multiplets of NiO, in correspondence to features observed in optical absorption spectra. Resonance enhancements of the triplet and singlet states resolved in energy confirm a spin-flip transition. Charge-transfer (CT) excitations are also clearly identified by resonance enhancement at photon energies corresponding to the satellites observed in the Ni L_2,3 X-ray absorption spectra.