Electronic spectra of uranyl chloride complexes in acetone: a CASSCF/CASPT2 investigation

Abstract

A theoretical study is presented of the electronic spectra of the complexes UO₂Cl₂ac₄, UO₂Cl₂ac₃, [UO₂Cl₃ac₂]⁻ and [UO₂Cl₃ac]⁻ (ac = acetone) using perturbation theory based on a complete-active-space type wavefunction (CASSCF/CASPT2). Both scalar relativistic effects and spin–orbit coupling were included in the calculations. The calculated excitation energies and oscillator strength values have been compared to the experimental absorption spectrum for uranyl chloride complexes in acetone solution, for chloride-to-uranyl ratios between two and three. The main purpose of this work was to investigate the origin of the remarkable intensity increase observed in the lower part of the experimental absorption spectra, upon addition of chloride to uranyl complexes in acetone. The calculated excitation energies for the different complexes are similar and closely correspond to the experimental data. However, in none of the theoretical spectra, the high intensities observed in the lower part of the experimental spectrum are reproduced.