The empty clathrate hydrate sII structure and its refilling with helium
The empty clathrate hydrate structure is the reference frame for predictions of gas hydrate properties and is of eminent importance as a reference point for our understanding of gas-water interactions in these guest-host compounds. In a previous experiment (5-25-217) we have attempted to form this empty hydrate structure by pumping out neon atoms of a neon-clathrate. We came quite close but due to scheduling constraints could not fully accomplish this task. We now propose to complete the emptying process and in this way form the lowest density form of condensed water known so far. Moreover, we would like to re-fill the empty hydrate structure with helium atoms to form for the first time a helium clathrate hydrate. Its structure and themal expansivity will be studied and compared to the empty hydrate as well as the structurally identical Ne-, Ar-, and Kr-clathrates. This will allow us to quantify the van der Waals interactions between water and the various noble gases in terms of the resulting volume changes. This then will provide valuable benchmarks for recent ab-initio attempts to better understand guest-host interactions in clathrates.
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KUHS Werner Friedrich; FALENTY Andrzej; Thomas C. Hansen and LAFOND Patrick. (2014). The empty clathrate hydrate sII structure and its refilling with helium. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-25-226
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