Methyl rotational potentials as a probe of the cage potential surface in methyl iodide clathrate

Methyl iodide water clathrates crystallize in the cubic II structure. Methyl tunneling spectra of CH3I identify three adsorption sites. The presence of 3 types of H-bonds in the cage surface are considered as likely origin. The barriers to rotation of methyl groups are low at all sites. Due to finite and different spin conversion times two of the three excited tunnel levels are not in thermal equilibrium. The classical methyl dynamics is almost unaffected by the weak potentials and described as rotational diffusion. A second slower quasielastic process may be interpreted as overall rotation of the molecule