Intensities of the vibrational spectra of siliceous zeolites by molecular dynamics calculations. II - Raman spectra

Three models based on electro-optical parameters were tested for the calcul ation of the Raman intensities of the vibrational modes deduced from (molec ular dynamics) calculations on four siliceous zeolites: sodalite, faujasite , zeolite A and silicalite. The best results were obtained from the electro -optical model containing three parameters: the derivatives of the longitud inal and transversal polarizabilities of the SiO bond with respect to the S iO bond length and the anisotropy of the polarizability tenser of the SiO b ond. These parameters permit the reproduction of the relative intensities o ver the whole wavenumber range. The bond stretching range over 700 cm(-1) i s driven by the first two parameters, whereas the equilibrium anisotropy pa rticipates significantly in the very low wavenumber region. Copyright (C) 2 001 John Wiley gr. Sons, Ltd.