Abnormal Thermal Expansion of Clathrate Hydrates Induced by Asymmetric Guest Molecules

摘要

We investigated for the first time the abnormal thermal expansion induced by an asymmetric guest structure using high-resolution neutron powder diffraction. Three dihydrogen molecules (H_(2), D_(2), and HD) were tested to explore the guest dynamics and thermal behavior of hydrogendoped clathrate hydrates. We confirmed the restricted spatial distribution and doughnut-like motion of the HD guest in the center of anisotropic sII-S (sII-S(velence)small cages of structure II hydrates). However, we failed to observe a mass-dependent relationship when comparing D_(2) with HD. The use of asymmetric guest molecules can significantly contribute to tuning the cage dimension and thus can improve the stable inclusion of small gaseous molecules in confined cages.