Raman spectroscopic study of the effectn of ion solvation on liquid phase structure and dynamics of LiI-acetone solutions

Electrolyte solutions of halide and perchlorate salts, mainly lithium, in non-aqueous solvent have attracted much attention in the past decades due to their employment in electrochemical field. Both ion–solvent and ion–ion interactions may contribute to the structure and dynamics of such systems at an ionic/molecular level, and their specific role depends on the involved species. Acetone is a widely-used solvent with fairly low electron donicity and relative permittivity, and these properties can account for the occurrence of ion aggregates along with single ions in solution. Lithium iodide is moderately soluble in acetone; with its strong -almost covalent- bonds, it is a good candidate to study the modulation of intermolecular (dipolar) interactions in acetone by ion addition. The vibrational spectroscopic investigation of electrolyte systems, such as LiI–acetone solutions at different concentration, constitutes an important approach to the study of solvation and association processes. Raman and depolarized Rayleigh scattering (DRS) are especially suitable for physicochemical studies in condensed phase allowing information to be obtained on system structure as well as molecular dynamics. Characteristic bands of acetone, namely carbonyl stretching, and CC symmetric stretching, are analysed to determine the effects of added salt in the solutions. Low frequency Raman spectra of LiI–acetone solutions will be presented and ion association in this system will be discussed for very low concentrations of the electrolyte.