experimentally by x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a
cryogenic ion trap. Three candidates, 6 Φ, 8 Φ, and 8 Γ, for the electronic ground state of Fe
2+ have been identified. These states carry sizable orbital angular momenta that disagree
with theoretical predictions from multireference configuration interaction and density
functional theory. Our results show that the ground states of neutral and cationic diatomic …