Paramagnetic and Optical Spectra of Divalent Nickel in Cubic Crystalline Fields

The paramagnetic resonance spectrum of divalent nickel in cubic MgO was investigated. The spectrum is isotropic with one line at $g=2.227\mathrm{}\pm 0.002$. Eight optical absorption lines at 8600, 13 400, 14 800, 21 550, 24 500, 25 950, 28 300, and 34 500 ${\mathrm{cm}}^{-1\mathrm{}}$ were detected. These absorption lines are interpreted as transitions between the singlet ground state and all possible Stark levels of the $F$, $P$, $D$, and $G$ levels. Agreement is obtained to within 300 ${\mathrm{cm}}^{-1\mathrm{}}$ by using crystalline field theory, with parameters $Dq=860\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $E_P=13\mathrm{}000$ ${\mathrm{cm}}^{-1\mathrm{}}$, $E_D=10\mathrm{}900$ ${\mathrm{cm}}^{-1\mathrm{}}$, $E_G=19\mathrm{}600$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $\lambda (\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{s}\mathrm{p}\mathrm{i}\mathrm{n}-\mathrm{o}\mathrm{r}\mathrm{b}\mathrm{i}\mathrm{t}\mathrm{c}\mathrm{o}\mathrm{u}\mathrm{p}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{t})=-245\mathrm{}$ (the spin-orbit coupling constant) = -245 ${\mathrm{cm}}^{-1\mathrm{}}$. The significance of the reduced values of the energy levels and the spin-orbit coupling constant is discussed.