Electron density topology of cubic structure I Xe clathrate hydrate at high pressure

In this report, we present a detailed powder x-ray diffraction study of the structural properties and charge density topology of structure I Xe clathrate hydrate under high pressure and room temperature. The pressure dependence of the structural parameters was determined by applying a Rietveld analysis to the experimental data. The combined Rietveld/maximum entropy method was used to derive the most probable charge density distribution at each pressure. Our results show that the charge density distribution of the encaged Xe atoms differs depending on the type of host cage at all pressures. Spherical electron density distributions were observed for the Xe atoms in the small cages while the atoms in the large cages showed longitudinal elongated electronic distributions. Along with the observed cage deformations, the change in electronic density distribution represents a clear indication that the guest-host interaction differs significantly between the small and large cages at high pressures. A similar behavior has been previously reported in low-temperature studies of methane clathrate hydrate.