Electron paramagnetic resonance spectrum of theΓ8ground state ofNp4+diluted inCs2ZrCl6

The electron paramagnetic resonance spectrum of ${\mathrm{Np}}^{4+}$ diluted in ${\mathrm{Cs}}_2$Zr${\mathrm{Cl}}_6$ is analyzed in terms of the theory formulated by Berlorizky et al. It is shown that if $g_J$, the Landé $g$ factor, is allowed to vary freely, a satisfactory fit may be obtained which is consistent with optical and EPR data obtained earlier on other tetrapositive actinide ions in the same host crystal. It is suggested that a better fit between the experimental data and the calculated spectrum may be obtained if the Zeeman mixing between the ground ${\Gamma }_8$ state and the excited ${\Gamma }_6$ state is considered.