Phase changes and intermolecular interactions of hydrogen hydrate

Abstract

Hydrogen hydrate is considered to be one of the major constituents of protostar, icy planets and their moons. A known high-pressure structure of hydrogen hydrate, filled ice Ic, is maintained to 60 GPa and shows the outstanding stability. In this study, the phase changes of hydrogen hydrate were clarified and the reasons for the remarkably stabilized structure with regard to the intermolecular interaction were examined. High-pressure experiments revealed that the suppress of the rotation of hydrogen molecules and partly extracting of hydrogen molecules occurred at around 20 GPa. These phenomena might occur in order to moderate unfavorable state caused by the close arrangement, leading the stability. At around 35 GPa, symmetrization of the hydrogen bond in the host water molecules occurred.