| Abstract
| - Visual observations through a microscope and in situ Raman measurements have been made for singlecrystalline ethylene hydrate (EH) and binary methane−ethylene hydrate (MEH) at pressures up to 3.7 GPaand room temperature. Both hydrates showed pressure-induced phase transitions at 1.6, 2.0, and 3.0 GPa forEH and at 1.7, 2.1, and 3.3 GPa for MEH. The cubic sI phase of EH and MEH remains stable up to 1.6 and1.7 GPa, respectively, which are more widely ranging values than the values for the methane hydrate sIphase. In this sI phase of binary MEH, the cage occupancies by methane and ethylene molecules are investigatedfrom Raman spectra. Above P = 3.0 GPa for EH and 3.3 GPa for MEH, they decomposed by associatingwith the formation of the polyethylene.
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