Hindered Rotation and Tunnelling of Adsorbed Species

Abstract

Hindered rotation and rotational tunnelling spectra can be used to study adsorbed systems in two ways. Firstly, they can give direct information about intermolecular forces. This is particularly important for adsorbed systems because, although there are few that are suitable for such measurements, we do not yet understand molecule-surface forces even for such a simple model adsorbent as graphite. Secondly, the spectra are sensitive to the surroundings of a molecule and can therefore probe its environment. In bulk solids this is not usually at all interesting because direct information about the structure will usually be available from diffraction. However, for adsorbed systems we are often not able to determine the structure of the surface, what site a molecule occupies when there is a choice, or even the structural relation between adjacent molecules. We give examples of both types of application in this paper.