Spin-dependent interactions inUv 5f2

The effects of the spin-dependent interactions on the energy-level scheme of $\mathrm{U}\mathrm{}\mathrm{v} 5f^2$ were investigated. The interactions considered were the spin-spin, the spin-other-orbit, and the effective electrostatic-spin-orbit (EL-SO) interactions. The values of the appropriate radial integrals were determined by using both ab initio and semiempirical methods. It is shown that the introduction of these interactions greatly improves the fit between observed and calculated levels and that the interaction mainly responsible for this improvement is the effective EL-SO interaction. Various properties of all known $4f^2$ (in lanthanides) and $5f^2$ (in actinides) configurations are compared. It is found that the spin-orbit and the effective EL-SO interactions are stronger in $\mathrm{U}\mathrm{}\mathrm{v} 5f^2$ as compared to $\mathrm{Pr}\mathrm{}\mathrm{IV} 4f^2$, whereas the "real" electrostatic and the mutual magnetic interactions are weaker. Similarly, the ratio of the strengths of the spin-orbit and the electrostatic interactions is larger in $\mathrm{Th}\mathrm{}\mathrm{III} 5f^2$ than in $\mathrm{La}\mathrm{}\mathrm{II} 4f^2$. Thus, in the actinides, and particularly in U v, the coupling tends more to intermediate coupling than in the corresponding lanthanides.