Clathrate nature of the high-pressure tetrahydrofuran hydrate phase and some new data on the phase diagram of the tetrahydrofuran-water system at pressures up to 3 GPa

Raman spectra of the internal vibrations of tetrahydrofuran molecules in two gas hydrate phases formed in the tetrahydrofuran-water system, as well as the spectra of solid and liquid tetrahydrofuran, under high-pressure conditions have been studied for the first time. A conclusion that the high-pressure hydrate is, most probably, of clathrate nature is made on the basis of spectral data. This hydrate is stable in the pressure range 0.49-3 GPa at room temperature. At a pressure of 3 GPa, the upper boundary (with respect to pressure) of the existence of the high-pressure hydrate is discovered. It corresponds to the decomposition of the hydrate into solid tetrahydrofuran and ice VII.