X-ray L(2,3) resonant Raman scattering from NiO: Spin flip and intermediate-state relaxation

We present measurements of x-ray resonant Raman scattering from NiO with L-2,L-3 excitation and calculations in an ionic model based on the process (2p(6)3s(2)3d(8))-->(2p(5)3s(2)3d(9))-->(2p(6)3s(1)3d(9)). The agreement between theory and experiment is good from below threshold up to 2.5-3 eV above threshold. By comparing theory and experiment, we show the effect of crystal-held splitting and the contribution bringing the Ni2+ triplet ground state to a singlet final state with excitation above the L-3 edge. When the excitation energy exceeds the L-3 threshold by about 3 eV, we present evidence that the intermediate state,in the scattering can also relax to a state similar to that created with threshold excitation. We suggest d-d excitation and electron-hole pair excitation as the origin of this relaxation.