The 5f3 manifold of the free-ion U3+: Ab initio calculations

The energy levels of the 5f3 manifold of the free-ion U3+ up to 30 000 cm−1 are calculated with two well stabilized ab initio methods based on the two-component Hamiltonians of Cowan–Griffin–Wood–Boring and Douglas–Kroll–Hess. Although the corresponding experimental data do not exist, estimates made out of experiments on the 5f3 manifold of U3+ in solids are usually referred to as the experimental energies of U3+ in gas phase. On the basis of a discussion on the available data of f-element ions in gas phase and in solids and a discussion on the expected precision of the present calculations, we suggest that the 5f3 energy levels of free U3+ are higher than the estimates and lower than the present ab initio calculations.