Splitting of the Ground Multiplet

Luminescence spectroscopy provides simple access to the splitting of the ground multiplet but this technique is not always accessible due to nonradiative decay and strong ligand absorptions as encountered, for example, in the [Ln(Pc)]-/0 systems. For these reasons, alternative spectroscopic tools should be available for magnetochemists. The use of INS as a spectroscopic probe for molecular magnetic systems has recently been reviewed by Guidi [36], Amoretti et al. [37]... 

For n> 7, the spin-orbit interaction stabilizes the maximal total momentum in the ground state, / = L + S [35]. Depending on the character of the splitting of the ground/-multiplet, the following situations may occur ... 

In a seminal contribution, Bleaney demonstrated that when the crystal-field splitting of the ground multiplet is smaller or comparable to kT, a situation often met with lanthanide complexes, the anisotropic part of the axial paramagnetic susceptibility tensor originates from second-order effects and can be simply estimated by the product of magnetic constants Cj, characteristics of the electronic configuration of each lanthanide (i.e., Bleaney factor), multiplied by the second-rank crystal-field parameter Bq (Eq. (34), Bleaney, 1972). 

Fig. 5. Crystal field splitting of the ground 3H4 multiplet of the U4+ ion in U02. The ground CF state of U4+ is a well-isolated T5 triplet.

The other interesting feature of eq. (40) is that the absolute value of Ep, will be lower for the F7/2 multiplet than for the Fj/2 level so that is enhanced. The widths of the excited level will also be increased by any increase in as is observed. One corollary of this suggestion is that 3 is probably the dominant component in the crystal-field splitting of the ground state manifold as well, in agreement with the suggestion of Levy and Zhang (1989). 

The expression (eq. 6.62) has assumed an equal population of the ground /-multiplet. For a paramagnet at a temperature well below the overall crystal field splitting of the multiplet, the 4f ions in the different eigenstates will be distributed randomly over the lattice sites with occupation numbers determined by the Boltzmann distribution. Since the 4f ions in these states have different cross-sections for conduction electron scattering, this contribution to the resistivity will be sensitive to changes in the population of crystal field levels. The... 

AEcf crystal-field splitting of the ground J multiplet chemical exchange characteristic time... 

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