Dodecahydrogen uranium: an icosahedral f-electron superatom with 26-electron shell structure
A new icosahedral superatom UH$_{12}$ is reported and analyzed using post-Hartree-Fock multiconfigurational methods. A RASSCF/CASPT2/RASSI/SINGLE_ANISO workflow is employed to determine the electronic energy levels and magnetic properties. Superatomic characteristics, such as orbital topologies and shell filling order, are discussed. The high hydrogen-to-uranium ratio and potential for optically stimulated decomposition make UH$_{12}$ worth investigation in the context of hydrogen storage. The electric-dipole transition oscillator strengths of the molecule vanish, while its lowest electronic transitions fall in the THz and infrared ranges. The lowest septet manifold exhibits crystal-field splitting into a 1+3+3 pattern, as expected from icosahedral symmetry. In turn, the interlevel gaps within these crystal-field triplets are 30-150 GHz (1-5 cm$^{-1}$). The molecule is magnetically isotropic at low fields, while its levels exhibit higher-order Zeeman anisotropy that becomes significant around 2 Tesla. These properties suggest potential relevance for quantum computing, quantum communication, and quantum memory, including qubit- and qudit-based architectures.