First-order Raman spectra have been measured at room temperature in five materials of the $D_{4h}$ point group: Ti${\mathrm{O}}_2$, Mg${\mathrm{F}}_2$, Zn${\mathrm{F}}_2$, Fe${\mathrm{F}}_2$ and Mn${\mathrm{F}}_2$. The experiments utilized an argon laser light source and photo-electric detection. The four Raman-active phonon frequencies, predicted by group theory to have symmetries $A_{1g}$, $B_{1g}$, $B_{2g}$, and $E_g$, were observed and classified in each material. Each spectrum exhibited strong lines of $A_{1g}$ and $E_g$ symmetries, a weak high-frequency line of $B_{2g}$ symmetry, and a very sharp $B_{1g}$ line at quite low frequency (less than 100 ${\mathrm{cm}}^{-1\mathrm{}}$ in all the materials except Ti${\mathrm{O}}_2$).

• Received 11 August 1966

DOI:https://doi.org/10.1103/PhysRev.154.522