Relativistic configuration interaction plus linearized-coupled-cluster calculations of ${\mathrm{U}}^{2+}$ energies, $g$ factors, transition rates, and lifetimes

Excitation energies, term designations, $g$ factors, transition rates, and lifetimes of ${\mathrm{U}}^{2+}$ are determined using a relativistic configuration interaction (CI) + linearized-coupled-cluster (LCC) approach. The CI-LCC energies are compared with CI + many-body-perturbation-theory (MBPT) and available experimental energies. Close agreement has been found with experiment, within hundreds of ${\mathrm{cm}}^{-1}$. In addition, lifetimes of higher levels have been calculated for comparison with three experimentally measured lifetimes, and close agreement has been found within the experimental error. CI-LCC calculations constitute a benchmark test of the CI + all-order method in complex relativistic systems such as actinides and their ions with many valence electrons. The theory yields many energy levels, $g$ factors, transition rates, and lifetimes of ${\mathrm{U}}^{2+}$ that are not available from experiment. The theory can be applied to other multivalence atoms and ions, which would be of interest to many applications.