Isotopic dilution study of self association in (CH3CN+CD3CN) mixture by scanning multichannel Raman difference technique and ab-initio calculations

The technique of scanning multichannel Raman difference spectroscopy was used to determine the precise wavenumber shifts of the ν1 (C–H)/(C–D) and ν2 (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.