Thermodynamic and Raman Spectroscopic Studies of Xe and Kr Hydrates

The thermodynamic stability boundaries for two noble gas (Xe and Kr) hydrates have been investigated in a pressure range up to 445 MPa and a temperature range of (324.4 to 345.3) K for the Xe hydrate system and (274.4 to 320.0) K for the Kr hydrate system. The Raman spectrum of the intermolecular O−O stretching vibration mode has been evaluated for each hydrate single crystal along with the three-phase coexisting curve. The slope change on the boundary curve and the pressure dependence on the Raman shift for the Kr hydrate crystal reveal that a structural phase-transition point exists at 414 MPa and 319.20 K, whereas the Xe hydrate crystal of structure I does not exhibit any phase transition over the region studied.