An Infrared Spectroscopic Study of Rotational Diffusion and Intermolecular Interactions In Acetonitrile

Several recent reviews1–3 have emphasised the current interest in the study of infrared band shapes in condensed phases. Potentially such data can provide very valuable information4–7 about the nature of the rotational and translational motions of individual molecules and about the intermolecular forces between them.7 However, because of the possible ambiguities arising in the interpretation of such data, (for example, there may be several contributions to the overall band shape7c,d) it is clear that detailed studies on simple, symmetrical molecules are required before studies on more complex systems are attempted. This has been generally recognised and a number of simple (mostly linear and symmetric top) molecules have now been studied4–10 in the compressed gas, liquid and solution phases. We have started a systematic study of simple nitriles and their weak molecular complexes. We report here some interesting data for the symmetric top molecule acetonitrile in the pure liquid and in solution in the “inert” solvent carbon tetrachloride. As far as we are aware the only previous work published on rotational diffusion in acetonitrile is the magnetic resonance work of Bopp.11