Inelastic X-ray scattering of synchrotron radiation at core resonances has turned soft X-ray emission spectroscopy into a new tool for probing the electronic structure of transition metal (TM) oxides at high resolution. In contrast to ordinary fluorescence, the ultimate achievable resolution is not restricted by the core hole life time at resonant excitation. We show that resonant inelastic X-ray scattering (RIXS) at TM oxide L-edges are a unique probe of charge-neutral crystal-field, so-called, dd-excitations. Here we discuss polarization resolved RIXS of the TM oxides La2CuO4, FeCO3, and alpha-Fe2O3. We find that the electronic structure at the TM ion sites may be described well by the ionic d(9), d(6), and d(5), respectively. The experimental RMS spectra are compared with atomic spectra using the appropriate ionic ground-state configurations and good agreement is found when the appropriate crystal symmetry is taken into account. In the case of La2CuO4 also charge transfer excitations are observed and show polarization dependence. We conclude that polarization resolved RMS allows accurate determination of energy positions and symmetry character of charge-neutral local excitations. (C) 2000 Elsevier Science B.V. All rights reserved.
