Concentration dependence of Raman linewidth of isopropanol in aqueous solution

Abstract The isotropic Raman linewidth of isopropanol at 818 cm −1 assigned to the CO stretching vibrational mode has been measured at a variety of concentrations in aqueous solution and in nonpolar tetrachloroethylene solution. On the basis of the concentration dependence of the linewidths observed in tetrachloroethylene solution, the isotropic Raman linewidth of the observed line is found to reflect the molarity of the hydrogen bonds of isopropanol. The unusual concentration dependence of the linewidths observed in aqueous solution, which shows a prominent maximum at a low concentration of isopropanol, has been examined in the light of these considerations. As a result, it is concluded that the concentration dependence of the linewidth is well explained in terms of the change in the partial molar volume of isopropanol, reflecting the change in the hydration structure in aqueous solution, and that the isotropic Raman linewidth of isopropanol is determined essentially by hydrogen bonding as an inhomogeneous broadening mechanism, other factors such as the vibrational dephasing being of less significance.

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