Unit-cell vibrational spectra of chromium trichoride and chromium tribromide

Raman spectra (at temperatures down to 4.2°K) and infrared spectra (at room temperature) of chromium trichloride and chromium tribromide have been obtained. Based on a factor group analysis and on the insensitivity of the CrCl₃ Raman spectrum to the monoclinic ā rhombohedral structural transformation, it is concluded that the spectra are characteristic of the unit cell of the diperiodic halogen-metal-halogen “sandwich” and not of the unit cell of the true triperiodic crystallographic space group.