Quantification and control of 5f versus 6d contributions to spin and orbital angular momenta in early actinide paramagnetism.

Computational studies indicate that both the 5f and 6d valence orbitals can actively participate in thorium and uranium bonding, and in certain ligand field environments, both 5f and 6d orbitals can carry unpaired electrons. Using M2,3-edge and M4,5-edge XMCD, it is possible to selectively probe 6d and 5f paramagnetism. We propose XMCD studies to investigate how spin-orbit coupling and 6d-5f spin-exchange can be tailored by the ligand-field environment. We specifically target linear and C3 symmetry U/Th molecules due to their propensity to support a 6dz21 ground-state electron occupation. By comparing references that support 6dz20 ground-states, we will be able to unravel the complex contributions to the paramagnetism of molecules with open-shell 6d and 5f orbitals. The results of this study will bring new and important insights into how oxidation state and coordination symmetry influence the paramagnetism of the early actinides.