Energy-dissipation of OH-stretching in tetrahydrofuran clathrate hydrate by Raman spectroscopy and DFT calculation

Temperature dependences of a Raman spectrum of a tetrahydrofuran clathrate hydrate (THF-CH) and an ice Ih are measured in 2800–3500 cm−1 from 4 to 250 K. A quality factor (Q factor) of a main peak at 3100 cm−1, which is assigned as an OH-stretching mode of H2O molecules, is discussed. An energy-dissipation of H2O molecules in the THF-CH is larger than that of the ice Ih for all temperatures in this study, since the THF-CH has the lower Q factor than the ice Ih. Molecular orbitals of a “THF-CH-like cluster” are calculated by density-functional theory to confirm a guest-host interaction in the THF-CH. HOMOs of the THF molecule and H2O molecules almost filled inside of a water-cage. This means that the THF interacts directly with H2O molecules of the water-cage. From the experimental and theoretical results, it is concluded that the direct guest-host interactions are the extra energy-dissipation channel of the OH-stretching mode in THF-CH.