FIGURE 2. Magic angle spinning ¹H NMR spectra of the THF + H₂ double hydrates formed at 120 bar and 270 K as a function of concentration of THF.

The NMR samples were prepared from deuterated water (D₂O, 99.9 at.% D) and THF (THF-d₈, 99.5 at.% D) by the same procedure as for Raman experiments. The chemical shifts of D₂O and THF-d₈ were identified from the NMR spectrum of THF-d₈ hydrate. Spectra were recorded using a Varian INOVA600 spectrometer, spin rate 12 kHz, pulse length 5 s, repetition time 15 s. The samples were transferred to an NMR rotor and analysed at 1 bar and 183 K. As the hydrate is not absolutely stable under these conditions, quantitative spectra cannot be obtained because of some decomposition, although a consistent picture can be constructed from the spectra that illustrate several features. The distribution of hydrogen molecules in both cages depends on temperature and pressure¹³.