Paramagnetic Resonance of Divalent Holmium in Calcium Fluoride

The paramagnetic resonance spectrum of the ground state of divalent holmium in calcium fluoride has been observed at a temperature of 4.3°K and at frequencies of 9 and 27 kMc/sec. The spectrum is isotropic and may be fitted to a spin Hamiltonian with $S=\frac{1}{2}$, $I=\frac{7}{2}$, $A=-0.1307\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $g=-5.912\mathrm{}$ and $G_N=+48\mathrm{}$, where $G_N$ is a pseudonuclear $g$ factor. The value of $g$ indicates that the ground state is ${\Gamma }_6$. The appearance of a pseudonuclear $g$ factor, which arises because the nearest quartet state has matrix elements with the ground state, permits a determination of the energy separation to the quartet state.