Sodalite from Vetralla (Roman potassic province) and Bancroft (Ontario, Canada): observed and simulated IR spectra

Infrared spectra of sodalites from Vetralla and Bancroft are compared to simulated spectra calculated from the available structural data and from empirical force constants applied to a simplified part-central-force potential-energy model. Calculation gives 18 vibrational modes including the 370 cm-1 mode observed by other authors in Raman spectra only. Increasing Si-O stretching constant implies variation of 3 high-frequency modes. The band group in the 750-650 cm-1 region comprises 3 modes strongly influenced by fal-o and subordinately by fsi-al. The 4 modes in the 500-350 cm-1 region are influenced by fo-si-o with weak contribution of O-oscillation, while the 295 cm-1 band is strongly influenced by fo-o, fNa-o and fal-o © 1991 Accademia nazionale dei Lincei.