Prediction of Vibrational Frequencies of UO22+ at the CCSD(T) Level

Electronic structure calculations at the coupled cluster (CCSD(T)) and density functional theory levels with various relative effective core potentials and basis sets have been used to predict the isolated uranyl ion frequencies. The effects of anharmonicity and spin-orbit corrections on the harmonic frequencies have been calculated. The anharmonic effects are larger than the spin orbit corrections and both are small. The anharmonic effects decrease the frequencies and the spin orbit corrections increase the stretches and decrease the bend. Overall, these corrections decrease the harmonic asymmetric stretch frequency by 6 cm-¹, the symmetric stretch by 3 cm-1 and the bend by 3 cm-¹. The splitting between the asymmetric and symmetric stretch is predicted to be 86 cm-¹, which is consistent with experimental trends for substituted uranyls in solution and in the solid state.