Dielectric and nuclear magnetic resonance study of the hydrate of sulphur hexafluoride

Abstract

In its dielectric and proton magnetic resonance behavior (except T1) the clathrate hydrate of SF6 is similar to ice I. Reorientation of water molecules appears to be little affected by the guest SF6 molecules and probably depends on the diffusion of rotational Bjerrum defects formed in numbers intrinsic to the lattice structure. The Arrhenius energy and activation entropy for dielectric relaxation are 12.3 + 0.5 kcal mole−1 and 6.8 + 2.0 cal deg−1 mole−1, respectively. The proton rigid-lattice second moment is 32.8 ± 0.5 G2 at −180 °C. The 19F second moment agrees with the value calculated for rapid isotropic rotation of SF6 molecules in the large cages only. Diffusion of water molecules in the hydrate is slower than in ice, which suggests that diffusion in ice occurs by migration of interstitial molecules through the channels in ice rather than by migration of lattice vacancies.