The technique of scanning multichannel Raman difference spectroscopy was used to determine the precise wavenumber shifts of the v(1) (C-H)/(C-D) and v(2) (C=N) stretching modes in (CH3CN + CD3CN) mixtures with respect to pure CH3CN/CD3CN as a function of concentration. A linear concentration dependence for C-H/C-D stretching modes indicates a dominant contribution of static fluctuations. A doublet structure in the C=N stretching band was explained in terms of self association, and to understand this phenomenon, ab-initio calculations were made to obtain the optimised geometries and vibrational wavenumbers of dimers in end-on and parallel configurations.