| Abstract
| - Clathrate hydrates consisting of HCFC (hydrochlorofluorocarbon) guest molecules within host water cagesrepresent a promising new medium for water desalination. The HCFC used in this study, 1,1-dichloro-1-fluoroethane (R141b), forms a structure II hydrate phase at mild conditions (0 °C, 0 atm). We present adetailed molecular picture of the structure and dynamics of guest R141b molecules within water cages, obtainedfrom ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Such information willbe needed to understand and control the nucleation and growth of these hydrates for industrial applications.Density functional theory calculations were used to provide an energetic and molecular orbital description ofR141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer,1,2-dichloro-1-fluoroethane, does not form at ambient conditions due to extensive overlap of electron densitybetween guest and host. Results for the isomer hydrate were supported by classical molecular dynamicssimulations and synthesis attempts. Molecular dynamics simulations show that R141b hydrate is stable attemperatures up to 265 K, while the isomer hydrate is only stable up to 150 K. Despite hydrogen bondingbetween guest and host, R141b molecules rotate freely within the water cage. The Raman spectrum of R141bin both the pure and hydrate phases is also compared with vibrational analysis from both computationalmethods. In particular, the frequency of a carbon−halogen stretch mode (585 cm-1) undergoes a shift tohigher frequency in the hydrate phase. Raman spectra also indicate that this peak undergoes splitting andintensity variation as the temperature is decreased from +4 to −4 °C.
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