Raman spectral studies on the structure of acetonitrile and its solutions with electrolytes and nonelectrolytes

Abstract

Raman spectra of acetonitrile is reported in its solutions with carbon tetrachloride, water, methanol, dimethyl sulphoxide (DMSO) and some electrolytes in C≡N stretching as well as in CH₃ stretching regions. Vibrational correlation functions are computed for the CH₃ stretching mode for varying concentrations of solutions. The vibrational relaxation times evaluated are also reported for these systems. It is found that association of acetonitrile through dipolar interactions is accompanied by an increase in intensity and a decrease in the frequency of C≡N band, whereas interactions through hydrogen bonding are accompanied by a decrease in intensity and increse in frequency. In the case of hydrogen bonding through methanol and also interactions through cations, new bands on the high frequency side appear, which are assigned to the complexed C≡N stretching bands. The CH₃ vibrational relaxation times are found to decrease on dilution for aqueous solutions of acetonitrile, whereas an increase in the vibrational relaxation times is found in the solutions of acetonitrile in CCl₄. In the case of solutions of electrolytes in acetonitrile, the vibrational relaxation times decrease with increasing concentration of electrolyte. The results are explained on the basis of the effect of complexation of C≡N on the CH₃ group.