A Theoretical Study of the Ground State and Lowest Excited States of PuO^0/+/+2 and PuO(2)^0/+/+2.

The ground and excited states of neutral and cationic PuO and PuO have been studied with multiconfigurational quantum chemical methods followed by second order perturbation theory{,} the CASSCF/CASPT2 method. Scalar relativistic effects and spin-orbit coupling have been included in the treatment. As literature values for the ionization energy of PuO are in the wide range of [similar]6.6 eV to [similar]10.1 eV{,} a central goal of the computations was to resolve these discrepancies; the theoretical results indicate that the ionization energy is near the lower end of this range. The calculated ionization energies for PuO{,} PuO and PuO are in good agreement with the experimental values.