The electronic spectra of UO2F2, both isolated and hydrated, have been studied using ab initio spin-orbit configuration interaction calculations based on relativistic effective core potentials. The structures of UO2F2 species were obtained by the density functional theory method. The initial structure has a (nonplanar) C-2v geometry, while adding solvating water molecules and optimizing the structure UO2F2H2O)(n) give a very stable structure for n = 4, with D-2 geometry. The ground state and some excited states were studied for UO2F2(H2O)(n) using the structures obtained. Electric-dipole transition moments were calculated for UO2F2(H2O)(4)Spin-orbit and equatorial -ligand (F-, H2O) interactions compete in determining the splittings of the known (3)Deltag state of the uranyl ion, particularly the 3 Delta (1g) luminescent state.