Interpretation of the Electric Field Effect on the Ground State Splitting of Mn⁺⁺ Ions in NaCl

The c S 5/2 ground state splitting of Mn ++ centres with an associated nearest neighbour cation vacancy in NaCl is calculated from a point ion model of the centre by using various theoretically proposed mechanisms. It is shown that the main contribution to the ground state splitting parameters results from a relativistic effect. The electric field induced changes of the ground state splitting are calculated from this mechanism. There are two contributions: 1. The combined effect of the external field and internal odd fields. 2. The change of the internal even fields from field induced relaxations of the centre. The results agree in sign and order of magnitude with the experimental data.