Magnetic circular dichroism and the electronic structure of the lowest excited states of the uranyl complexes.

Abstract

The magnetic circular dichroism (MCD) spectrum of the uranyl ion was measured over the range 20, 000-35, 000 cm-1 for several uranyl complexes of different symmetries. The nature and structure of the lowest-energy bands vary to a greater extent with symmetries of the complex ions. However, the interaction energy against uranium 5f orbitals of the equatorial ligand field perpendicular to the O-U-O axis could be reasonably estimated by means of the angular overlap approximation. The Faraday parameters obtained from analysis of the MCD and absorption spectra were reproduced by theoretical calculations taking into account of spin-orbit couplings and the equatorial ligand-field interactions. Thus it was concluded that the lowest excited states of the uranyl moiety arise from one-electron excitations of singlet-triplet charge-transfer from the 1.πg orbital mainly localized on the oxygen atoms to 5f orbitals centered on the uranium atom namely 1∑g+→3Γu, 1∑g+→3Δu and 1∑g+→3Φu.