Tetrahydrofuran Clathrate Hydrate Formation

We report on the formation of tetrahydrofuran clathrate hydrate studied by x-ray Raman scattering measurements at the oxygen $K$ edge. A comparison of x-ray Raman spectra measured from water-tetrahydrofuran mixtures and tetrahydrofuran hydrate at different temperatures supports stochastic hydrate formation models rather than models assuming hydrate precursors. This is confirmed by molecular dynamics simulations and density functional theory calculations of x-ray Raman spectra. In addition, changes in the spectra of tetrahydrofuran hydrate with temperatures close to the hydrate’s dissociation temperature were observed and may be connected to changes in hydrate’s local structure due to the formation of hydrogen bonds between guest and water molecules.

Figure 1

Experimental XRS spectra at the oxygen $K$ edge for the liquid mixture and the hydrate at different temperatures. The spectra are divided in a preedge (I), main edge (II), and post-edge (III) region.

Figure 2

Differences of the XRS spectra as indicated. A comparison with calculated spectra (DFT) and the temperature effect of water (Ref. 14) is also shown.