Quadrupole Interactions of Vanadium and Manganese in Corundum

Hyperfine fields and quadrupole interactions have been measured for divalent vanadium and quadrivalent manganese in corundum by electron-nuclear-double-resonance (ENDOR) spectroscopy. This work, together with previous work on trivalent chromium, provides a study of electronic properties of dilute impurities in an isoelectronic sequence. The results show that the internal magnetic field due to the paramagnetic electrons is the same for all ions and equal to about -200 kG. The quadrupole interaction is -0.021 Mc/sec for ${\mathrm{V}}^{51}$ and 0.138 Mc/sec for ${\mathrm{Mn}}^{55}$. This is to be compared with a value for the host aluminum nuclei of 0.180 Mc/sec. A theory based on the point-charge model is unable to account for this result in any simple way. The possible influence of covalent bonds on the observed field gradients is discussed.