Single-crystal Raman studies and the vibrational spectrum of the dithionate ion

Abstract

A factor-group analysis of Na₂S₂O₆,2H₂O is described in detail. Unambiguous assignment of the Raman-active factor-group fundamentals follows from the single-crystal Raman observations. The relative magnitudes of the components of the derived polarizability tensor for all six Raman-active modes of the dithionate ion are calculated on the basis of the oriented gas-phase approximation. From these values the depolarization ratios for the Raman-active fundamentals of the S₂O₆^2– ion in aqueous solution are calculated, together with relative intensities of the Raman-active fundamentals in the solution spectrum and in the powder spectrum. On the basis of the ℒ-matrix derived from the vibrational analysis, together with the use of the δ-function model, derivative mean polarizability values are calculated. The powder i.r. and Raman spectrum of Na₂S₂O₆,2H₂O is reported together with the aqueous solution Raman spectrum of this compound. The agreement between observation and calculation is excellent, although the data derived from the δ-function model are open to criticism.