Ordering of guest-molecule dipoles in the structure I clathrate hydrate of trimethylene oxides

The rotational mobility of encaged trimethylene oxide (TMO) molecules was studied down to 1.8°K by sub-MHz dielectric measurements of the structure I H₂O clathrate and by proton magnetic resonance measurements of the corresponding D₂O clathrate. The results indicate that below a transitional temperature range about 105°K most TMO dipoles assume parallel alignment along the $\text{4}$ axes of the cages. Below the transition the proton second moment suggests the presence of hindered rotation of TMO about its polar axis until the rigid-lattice condition is reached below 5°K. Some residual very broad dielectric absorption (activation energy 2.1 kcal/mole) persists to very low temperatures. Guest-guest and guest-host interaction energies are calculated for simple models