Calculation of electronic spectra of hydrated Ln(III) ions within the INDO/S-CI approach

We present INDO/S-CI model calculations including a spin-orbit treatment on the electronic absorption spectra of the trivalent lanthanide ions Pr³⁺, Nd³⁺, and Tm³⁺ in aqueous solution. With this molecular orbital based procedure both the experimental transition energies and the relative oscillator strengths of the 4f → 4f excitations in the 8- and 9-fold coordinated complexes [Ln(H₂O)_n]³⁺ are well reproduced. The intensities of the transitions are due to the admixture of higher lying configurations into the 4fⁿ ground state which is found already at the SCF level.