Electronic structure of MgF2: Co++

The F19 superhyperfine structure of the EPR spectra of Co++ in MgF2 is interpreted with simple molecular-orbital theory. A necessary preliminary analysis is made of the g tensor and of the spacing of the six Kramers doublets derived from the T14 ground manifold. The ligand-field parameters of the rhombic field, Δ≅510 cm-1 and Γ≅-390 cm-1, and the spin-orbit coupling, λ≅-157 cm-1, are significantly different from values derived from less complete data. The reported superhyperfine interactions provide sufficient data to determine, without recourse to much less certain orbital-reduction factors, the s-, sigma-, and pi-bonding fractions: fs=(0.61±0.02)%, fσ=(3.9±0.3)%, and fπ=(0.9±0.3)% for the two equivalent fluorine ions along [110]. For the other four fluorine ions similar estimates are obtained. These results are at variance with the suggestion, made for octahedral Co++, that sigma and pi bonding are of comparable magnitude. © 1966 The American Physical Society.