Electronic structure of americium sesquioxide probed by resonant inelastic x-ray scattering

The Am 5d-5f resonant inelastic x-ray scattering (RIXS) data of americium sesquioxide were measured at incident photon energies throughout the Am O4,5 edges. The experiment was supported by calculations using several model approaches. While the experimental Am O4,5 x-ray absorption spectrum of Am2O3 is compared with the spectra calculated in the framework of atomic multiplet and crystal-field multiplet theories and Anderson impurity model (AIM) for the Am(III) system, the recorded Am 5d-5 f RIXS data are essentially reproduced by the crystal-field multiplet calculations. A combination of the experimental scattering geometry and theoretical analysis of the character of the electronic states probed during the RIXS process confirms that the ground state of Am2O3 is singlet P1. An appearance of the low-intense charge-transfer satellite in the Am 5d-5 f RIXS spectra at an energy loss of similar to 5.5 eV suggests weak Am 5 f-O 2p hybridization which is in agreement with AIM estimations of the 5 f occupancy from spectroscopic data in Am2O3 as being 6.05 electrons.