Local structure of guest molecules in gas hydrates--a model study of Kr and Xe clathrates

Gas hydrates constitute a class of solids in which small molecules occupy cavities inside an ice-like structure. There is enormous scientific and technological interest in understanding the structure, stability and formation mechanism of clathrates. We developed and constructed a variable temperature high-pressure cell for x-rays measurements, which allows in situ studies of clathrate formation or decomposition. We used XAFS and Diffraction techniques to study the evolution of the structure during formation and decomposition. We studied two clathrates structures, structure I (Xe) and structure II (Kr). We were able to identify the local structure around the guest atom. We identified the rare gas-water complexes that act as precursor to the formation of the crystalline phases. We observed the transformation of the clathrate from structure II to structure I when Xe is added to Kr clathrates.