Paramagnetic Resonance of Divalent Praseodymium in Calcium Fluoride

Abstract

The electron paramagnetic resonance spectra of ${\mathrm{Pr}}^{++}$ in the cubic field of Ca${\mathrm{F}}_{2}$ was obtained at 24 kMc, at liquid-helium temperatures. As predicted by Lea, Leask, and Wolf, the measurements show that the ground state of ${\mathrm{Pr}}^{++}$ is ${\ensuremath{\Gamma}}_{8}$. We estimate their parameter $x$ to be -0.55 for ${\mathrm{Pr}}^{++}$, which is in line with data on other ions in Ca${\mathrm{F}}_{2}$. Extensive and complicated hyperfine structure was detected in addition to the fine-structure splitting of the ${\ensuremath{\Gamma}}_{8}$ state but no analysis is made of it. Since the hyperfine splitting was not small relative to the Zeeman splitting, normally forbidden $\ensuremath{\Delta}{m}_{I}=\ifmmode\pm\else\textpm\fi{}1$ transitions were also observed.