Low- and very-low-frequency dynamics in ZnCl2aqueous solutions: a comparative investigation by Raman, Rayleigh wing and inelastic neutron scattering

The authors report the results of a comprehensive investigation on the low ( omega <or approximately=400 cm-1) and very low (0.2 cm-1) and very low (0.2 cm-1<or approximately= omega <or approximately=40 cm-1) frequency vibrational and structural dynamics in water and aqueous solutions of ZnCl2 (for concentrations up to saturation). Time-of-flight inelastic neutron scattering and Raman spectroscopy were used to obtain the vibrational frequency distributions and the frequency dependence of the Raman electron-vibration coupling function. Structural relaxation times were determined by depolarised Rayleigh wing scattering. The results, which confirm that these systems are best viewed as locally amorphous solids, are discussed in terms of locally ordered, dynamically correlated patches in which structure and dynamics are strongly influenced by the solute, especially by its action of the water hydrogen bond.