The Raman spectrum and analysis of phonon modes in sodalite

Polarised Raman spectra of chloro- and bromo-sodalite (Na 4 Al 3 (SiO 4 ) 3 Br) 2 single crystals have been recorded, and 28 of the predicted 32 Raman-active phonon modes observed. A full group-theoretical analysis of the zone-centre phonons is given. The internal modes are assigned using as a basis the normal mode frequencies of the XO 4 complex (X=Si or Al). A 'super-lattice' approximation has enabled qualitative predictions to be made about the intensities of the Raman Raman and infrared modes, leading to a consistent model for the interpretation of the Raman spectrum of the infrared spectrum of Henderson and Taylor (1977-8).