  Novel ground states might be realized in honeycomb lattices with strong
spin-orbit coupling. Here we study the electronic structure of
${\alpha}$-RuCl$_3$, in which the Ru ions are in a d5 configuration and form a
honeycomb lattice, by angle-resolved photoemission, x-ray photoemission and
electron energy loss spectroscopy supported by density functional theory and
multiplet calculations. We find that ${\alpha}$-RuCl$_3$ is a Mott insulator
with significant spin-orbit coupling, whose low energy electronic structure is
naturally mapped onto Jeff states. This makes ${\alpha}$-RuCl$_3$ a promising
candidate for the realization of Kitaev physics. Relevant electronic parameters
such as the Hubbard energy U, the crystal field splitting 10Dq and the charge
transfer energy are evaluated. Furthermore, we observe significant Cl
photodesorption with time, which must be taken into account when interpreting
photoemission and other surface sensitive experiments.
