Dynamics and adsorption sites for guest molecules in methyl chloride hydrate

Methyl rotational tunneling, quasielastic spectra and phonon densities of states measured with neutrons at energy transfers from 35 mu eV to 40 meV are used to characterize the adsorption sites and potentials of CH(3)Cl guest molecules in the two kinds of cages of cubic I methyl chloride hydrate. The model of adsorption to hydrogen bonds of the ice cage explains the broad tunnel spectrum as a superposition of four bands. Up to a temperature T similar to 80 K the quasielastic scattering is influenced by quantum motion. Only above T similar to 80 K does the effective linewidth follow an Arrhenius behavior with an average activation energy. Rotational potentials contain a significant sixfold component supporting the proposed adsorption to hydrogen bonds with their mirror symmetry. Positional disorder of protons in the hydrogen bonds of the host ice lattice leads to potential distributions of large relative widths delta V/(V) over bar <= 0.35.