Hydrogen-bonding and self association investigated in the binary mixture (C6H5CN + CH3OH) via concentration dependent Raman study of the CN stretching mode of benzonitrile (C6H5CN) and ab-initio calculations

The Raman study of (C6H5CN + CH3OH) binary mixture has been presented. The isotropic part of the Raman spectra, Iiso are analyzed in the CN stretching region. For neat C6H5CN, the Iiso shows a double peak structure, which has been explained in terms of self association. A quantum chemical calculation on the optimized structures and wavenumbers of different modes of neat C6H5CN, self associated C6H5CN and the hydrogen-bonded C6H5CN⋯HOCH3 complex reveals that the wavenumber position of the CN stretching mode is blue shifted due to both the self association and the hydrogen-bonding with CH3OH. The Raman spectra of binary mixtures with different mole fractions of the reference system (C6H5CN), C = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, as well as neat liquid have been explained in terms of self association and hydrogen-bonding. A variation of intensity ratio of the peak assigned to the hydrogen-bonded complex to the main band with concentration exhibits a regular trend. The dephasing of the CN stretching mode in the free C6H5CN molecules seems to be governed predominantly by the concentration fluctuation model, but other effects like diffusion and motional narrowing may also have some small influence.