Rayleigh and Raman light scattering in hydrogen-bonded acetonitrile–water

Abstract.

The structure, vibrational frequencies, light scattering activities and binding energies of CH₃CN⋯H₂O are obtained from ab initio methods. The hydrogen N⋯H bond distance is calculated as 2.06 Å, the dipole moment as 5.77 D and our best estimate for the binding energy is 3.5 kcal mol⁻¹ (14.7 kJ mol⁻¹), after correcting for zero-point vibrations. The calculated average dipole polarizability is 39.67 au and the anisotropy is fairly large, corresponding to 21.78 au. The changes in intramolecular vibrational frequencies are analyzed. The scattering activities and depolarization of the Rayleigh and Raman light scattered are calculated. In the Raman case the depolarization due to the intense NC stretching vibration is increased by 20% after the hydrogen bond. For the OH symmetric stretch of water there is a large redshift of 75 cm⁻¹ and a great intensification of the Raman scattering activity by a factor of 2 and a considerable increase of the depolarization by a factor of nearly 4.