Investigation of the low-lying excited states of PuO22+

We present a theoretical study of the first low-lying excited states of plu tonium, Pu(VI)O-2(2+). Their geometries were optimized and found to be basi cally unchanged due to the local character of the excitations. Vertical spi n-free excitation energies were calculated for all (23) states below 240 kc al/mol. Fine-structure levels were obtained for all states in the f-manifol d below 105 kcal/mol. The ground state of the plutonyl(VI) ion is a H-3(g) at the spin-free level, and its Ohm=4 component at the spin-orbit level. Th e spin-orbit interaction was calculated at the quasi-degenerate perturbatio n level, using 'the one-to-one correspondence of the integrals' method prop osed, combined with a shift technique. We propose a simpler approach avoidi ng the use of generalised contracted ECP basis sets. This is, to our knowle dge, the first systematic study of the low-lying excited states of the plut onyl ion including spin-orbit effects. (C) 1999 Elsevier Science B.V. All r ights reserved.