Charge-current contribution to low-frequency Raman scattering from glass-forming ionic liquids

A low-frequency Raman study on the fragile ionic glass-forming system 2BiCl (3)-KCl is reported. Approaches that are usually followed for a quantitativ e interpretation of the frequency and temperature dependence of the spectra have been employed. The inadequacy of satisfactorily fitting the experimen tal data applying standard models has led to the introduction of an extra c ontribution having its origin in scattering caused by charge-current fluctu ations. The frequency dependence of the depolarization ratio, which is usua lly overlooked in low-frequency Raman studies, is another fact that reveals the necessity of the approach followed. We put forward a partial depolariz ation ratio analysis of the individual contributions involved in the low-fr equency Raman spectrum. The characteristic frequency dependence of the depo larization ratio that each component exhibits is discussed alongside the co rresponding physical mechanism on which the particular scattering contribut ion originates. Although applicable only to ionic glass-forming systems thi s picture stems from a well-grounded physical basis and may aid towards a b etter comprehension to selected aspects for supercooled liquids.