Study of aqueous acetone solution at various concentrations : low-frequency Raman and molecular dynamics simulations
Résumé
The low-frequency Raman spectra of pure water, pure acetone, and their mixtures at different proportions have been analyzed. New experimental (low-frequency Raman spectra) and calculations (molecular dynamics simulations) show that the band observed at 60 cm-1 in the low-frequency Raman spectra of water is associated with the oscillation of a water molecule within the cage formed by its neighbors. On the basis of this model, an analysis has been made of the variation of the position and width of the band assigned to intermolecular oscillations. The influence of the acetone concentration on this feature has been analyzed, and its interpretation has been proposed. The position of the peak at 60 cm-1 has a nonlinear dependence on the mole fraction of acetone. On the hypothesis that the translational dynamics of water contributes mainly to the low-frequency Raman spectra, the shift to higher frequencies of the peak at 60 cm-1 is interpreted as an indication of the stiffening of the cage formed by the neighboring molecules. The shift of the peak at about 190 cm-1 to lower frequencies and the nonlinear concentration dependence of its width is an indication that acetone acts as a water structure breaker.