Ab initio studies of excited states of polyatomic molecules including spin-orbit and multiplet effects: The electronic states of UF6

The excited electronic states of UF6 between 3--10 eV are investigated by ab initio configuration interaction (CI) calculations using a relativistic effective core potential (RECP) on the uranium and nonrelativistic ECP's on the fluorines. Spin-orbit coupling effects are incorporated by diagonalizing an effective one-electron operator over the CI wave functions. This represents one of the first studies of polyatomic molecules to treat both spin-orbit effects and multiplet effects arising from electron--electron interactions. A detailed analysis of the electronic states of UF6 is given both with and without spin-orbit coupling effects. Assignments for the major peaks in the 3--10 eV energy range are given, as aided by recent electron impact studies. Comparisons are made between the present many-electron states and previous one-electron theoretical treatments