Circular dichroism spectra and electronic rotatory strengths of the samarium 4f → 4f transitions in Na₃[Sm(oxydiacetate)₃]·2NaClO₄·6H₂O

Abstract

Axial absorption and circular dichroism (CD) spectra are reported for single crystals of Na₃[Sm(oxydiacetate)₃]·2NaClO₄·6H₂O over the spectral region 17 600–30 500 cm^-1. Within this region, 213 individual (4f → 4f) crystal-field transitions may occur from the ground crystal-field level of Sm³⁺. Each of these transitions is both electric-dipole and magnetic-dipole allowed in the axial spectra (according to D ₃ site-symmetry selection rules), and each is predicted to be optically active (i.e., circular dichroic). Rotatory strengths, determined from low-temperature CD measurements, are reported for 52 of these transitions, and dissymmetry factors are reported for 39 of the transitions. Each of the 52 transitions (for which empirical rotatory strengths are reported) is assigned and characterized with respect to the symmetries of the connecting crystal-field levels and their principal 4f ⁵ multiplet parentages. Calculations of rotatory strengths, dipole strengths, and dissymmetry factors are reported for transitions spanning the entire 17 600–30 500 cm^-1 region. These calculations are based on a general parametric model for 4f ^N energy levels and lanthanide-ligand-radiation field interactions (within the one-electron/one-photon approximation). This model yields excellent fits between calculated and experimentally observed 4f → 4f transition energies, dipole strengths, rotatory strengths, and dissymmetry factors for Sm³⁺ in Na₃[Sm(oxydiacetate)₃]·2NaClO₄·6H₂O. This is the first study in which lanthanide chiroptical properties have been quantitatively measured, analysed, and characterized over a wide spectral range spanning a large number of 4f → 4f crystal-field transitions.