The electronic structure, spectra, and magnetic properties of actinyl ions: Part I. The uranyl ion

Abstract

A calculation of the 1-electron MO energy levels of UO 2 ++ has been carried out using rough estimates of overlap integrals of a set of a Slater orbitals presumed to correspond to the relevant oxygen and uranium atomic orbitals. It is shown that the ground state of a weak uranyl ion is most probably 1 Σ g + and that the UO bond order is three. It is suggested that the variation of the UO bond length in the UO 2 ++ entity, and the decrease of the antisymmetric and symmetric vibrational stretching frequencies should condition a ligand spectrochemical series. A discussion of the spectrum of the uranyl ion is presented in terms of a Hund's coupling case (a) molecule. It is shown that the visible absorption band of the UO 2 ++ ion most probably contains three distinct electronic transitions, which are the components of a T ← S process. The lifetime of the emission process as calculated from the reverse absorption is 4.76 × 10 −4 sec; as calculated using a spin-orbital perturbation operator it is of the order of 10 −4 – 10 −5 sec; the experimental value ranges from 1 × 10 −4 to 7 × 10 −4 sec. It is also shown that the transition is of an approximate charge-transfer type, and the use of the term “phosphorescence” for the emission process is advocated. A discussion of magnetic susceptibility and its anistropy is also presented