The origin of the zerohyphen;field splittings of the orbitally nondegenerate ground states of the transition metal ions (3d3, 3d5, and 3d8solutes) has been studied on the assumption that these splittings are due to the combined action of an electric field gradient and the spinmdash;spin interaction. A relation between the splitting parametersDandEof the conventional spin Hamiltonian and the field gradientsqverbar; verbar;andeegr;qverbar; verbar;, respectively, has been deduced on the above basis using hydrogenic wavefunctions anddrarr;d,drarr;g, anddrarr;sexcitations. A reasonably good agreement with the splitting has been obtained for Mn2+in corundum but an apparent disagreement has been found for Fe3+in Al2O3, considering the known values of the field gradients in these cases. For Cr3+(d3solute) and Ni2+(d8solute) in corundum, the major sources of splitting seem to be the spinmdash;orbit interaction and the distortion of the ground state wavefunctions due to covalent pgr; bonding and not the spinmdash;spin interaction. The cause of the apparent disagreement for Fe3+in Al2O3is discussed. A definite understanding of the cause of the zerohyphen;field splittings in the transition metal ions depends on more accurate knowledge of the field gradients acting on these ions in different crystalline environments.
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