Measuring mixed-valence thorium metal-metal bonding with valence-to-core L3-edge RIXS

We recently reported the first example of thorium–thorium bonding in a crystalline cluster. Crystallography analysis and DFT results show the cluster exhibits a diamagnetic, closed-shell singlet ground state with a valence-delocalized three-thorium-two-electron σ-aromatic bond. The frontier molecular orbitals are predicted to be predominantly 6d in character, with a triplet excited state lying 0.95 eV above the ground state. We therefore propose valence-to-core RIXS studies to directly access these states with high energy resolution. To benchmark our results, measurements on a series of thorium organometallic compounds are also proposed, including classic metallocene molecules that astonishingly have yet to be studied by L3-edge RIXS.