  The Am $5d$-$5f$ resonant inelastic x-ray scattering (RIXS) data of americium
sesquioxide were measured at incident photon energies throughout the Am
$O_{4,5}$ edges. The experiment was supported by calculations using several
model approaches. While the experimental Am $O_{4,5}$ x-ray absorption spectrum
of Am$_2$O$_3$ 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 $5d$-$5f$ 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 Am$_2$O$_3$ is singlet $\Gamma_1$. An appearance of
the low-intense charge-transfer satellite in the Am $5d$-$5f$ RIXS spectra at
an energy loss of $\sim$5.5 eV, suggests weak Am $5f$-O $2p$ hybridization
which is in agreement with AIM estimations of the $5f$ occupancy from
spectroscopic data in Am$_2$O$_3$ as being 6.05 electrons.
