Electronic Energy Levels of the Lighter Actinides: U3+, Np3+, Pu3+, Am3+, and Cm3+

The results of a systematic theoretical and experimental study of the energy levels of the lighter actinides, U3+ through to Cm3+, in various solution media is reported. Calculations of the ``free-ion'' levels have been made for all these ions and compared with the observed absorption bands. A clear correspondence is found for most of the lower levels. The actinides have been found to show very large departures from Russell—Saunders coupling with spin—orbit constants approximately twice those of the corresponding lanthanides. A pronounced tendency towards jj coupling is noted and its consequences discussed.