Molecular motion in a model of liquid acetonitrile

Abstract

Molecular dynamics calculations have been carried out for a model of liquid acetonitrile. Results are reported for correlation functions appropriate to infrared, Raman and N.M.R. measurements, and very good agreement with experiment is found. Both the tumbling and the spinning motion of the molecule have been studied and the results are used to discuss the choice of nuclear quadrupole coupling constant in the analysis of T ₁ measurements, the interpretation of N.M.R. data in terms of diffusion coefficients, vibrational relaxation and Coriolis coupling for the perpendicular Raman bands, and the validity of the J diffusion model. The tumbling motion is similar to the motion seen in many organic liquids, with evidence of a cage effect. The spinning motion is also hindered, but the reorientation is faster and there is no apparent cage effect. The characteristic, non-lorentzian lineshape of the perpendicular infrared and Raman bands of CH₃X molecules is recovered; the associated correlation times show a significant isotope effect.