The pure nuclear quadrupole resonance frequencies of ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ nuclei in ${\mathrm{Cu}}_2$O have been measured from 350 down to 4°K. Below 140°K the dependence deviates from linearity. A model based on vibrations of the Cu nuclei transverse to the O-Cu-O axis is shown to be consistent with the experiments. The frequency $\omega$ of the transverse vibrational band is derived to be 97±7 ${\mathrm{cm}}^{-1\mathrm{}}$.

• Received 15 April 1966

DOI:https://doi.org/10.1103/PhysRev.150.200