Ground states degeneracy lifting

The degeneracy of the ground state is lifted, and at low temperatures there is a slow electronic relaxation between levels. A Jahn-Teller effect need not be invoked. The theory evolved to interpret the MgO data has led to a method for determining the quadrupole moment of Fe (see Chapter 5) [52]. 

An applied stress lowers the symmetry of the crystal and can make defects with different orientations inequivalent. A review of stress techniques has been written by Davies (1988). The degeneracy of the ground state and also of the spectroscopic transition energies can be lifted. In this section we suppose that the defects cannot reorient and consider only the splitting of the transition energies. The stress-induced reorientation of defects is discussed in the next section. 

Liehr has shown (142) that the orbital degeneracy of the ground state in a tetrahedral nickel(II) complex may be lifted by spin-orbit coupling. This means that these complexes may not be liable to Jahn-Teller distortion as has been thought for some time. Such coupling would also have the effect of splitting all transitions into several components, the exact number... 

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