Amorphous SF6 hydrate (SF6·17H2O) was prepared by depositing the mixed vapor onto a substrate kept at about 8 K. The inelastic neutron-scattering spectra of the as-deposited sample and those annealed at about 120 and 150 K were measured at 50 K in the energy range below 100 meV. The first two samples were considered to be in amorphous states while the third one was in a crystalline state. The librational frequency of the water molecule (at around 60 meV) is smaller in the order of (as-deposited sample) < (annealed sample) < (crystalline sample). This indicates that the strength of the intermolecular hydrogen bonds is (crystalline sample) > (annealed sample) > (as-deposited sample). The spectra below 10 meV were compared with our previous data of pure vapor-deposited amorphous ices and those doped with methanol (CD3OH). The low-energy excitation (E < 6 meV) differed drastically depending on the dopants, i.e., the scattering intensity was enhanced by methanol doping but reduced by SF6 doping. This may be because the hydrogen-bond formation was hindered by methanol doping but promoted rather more by SF6 doping because of the hydrophobic interaction as in clathrate hydrates. PACS Nos.: 61.12Ex, 63.50tx
Low Energy Excitation Spectra of Trapped Bose Condensates
