NMR approach of the electronic properties of the hydrated trivalent rare earth ions in solution

Abstract:

The electronic properties of the lanthanide ions are systematically investigated through the NMR of the protons of the tetramethylammonium ion , used as a probe in solution. The effective magnetic moments on the ions are obtained by measuring the paramagnetic shift of the proton resonance line due to the demagnetizing field that is proportional to the rare earth concentration. These results allow to estimate the sizes of the total splitting of the crystal field acting on the ground multiplet of the various lanthanides. The measured intermolecular longitudinal relaxation rates of the protons are compared with the computed values, both of the usual Solomon theory and of the Curie mechanism. The measured values are intermediate between those predicted by the two theories. This allows a rather accurate determination of the lifetimes of the electronic levels of the ions, as they little depend on the details of the description for the relative spatial microdynamics of the / repulsive ion pair.