Spectres Raman d'un Monocristal de As2O3, SO3 et Calcul du Champ de Force

Abstract

AbstractThe polarized Raman spectra of a single crystal of As2O3, SO3, along with the infrared spectra of this compound in the polycrystalline state have been investigated at 30 K and 300 K in the 20–4000 cm−1 range. The dependance of the frequency shift of polar vibrations with the geometry of the Raman experiments has also been studied. An assignment in terms of symmetry species is proposed for 49 of the 51 expected active modes. A normal coordinate calculation using a valence force field has been performed for the principal vibrations (k ⋍ 0) of the crystal. The good agreement between observed and calculated frequencies shows that long range forces are negligible compared to internal valence forces. There are two different SO bonds characterized by stretching force constants of 9.1 and 5.2 mdyn Å−1 and SO bond lengths have been estimated equal to 1.44 and 1.56 Å respectively, by using an empirical correlation. The AsO stretching force constants of the OAsOAs…︁ chains and of the bonds linking As and SO4 groups are similar: 2.0 and 1.9 mdyn Å−1 respectively. Therefore the crystal is not an ionic sulphate compound.