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Raman spectra of ethane trapped in the small 5 12 cage of sII hydrate (at ∼70 MPa), isobutane trapped in the large 5 12 6 4 cage of sII hydrate, and the gauche form of n-butane trapped in the large 5 12 6 4 cage of sII hydrate were obtained for the first time. These new Raman results are combined with existing Raman and IR results for various guests to infer general trends in vibrational frequencies of guest molecules trapped in clathrate hydrate cages as a function of cage size, guest size, guest vibrational mode, and pressure. The observed trend in stretching frequencies of guests with cage size, which can be stated as "the larger the cavity, the lower the frequency", is explained through the qualitative "loose cage-tight cage" model of Pimentel and Charles (Pure Appl. Chem. 1963, 7, 111).

In the Prausnitz tradition, molecular and macroscopic evidence of hydrate formation and kinetic inhibition is presented. On the microscopic level, the first Raman spectra are presented for the formation of both uninhibited and inhibited methane hydrates with time. This method has the potential to provide a microscopic-based kinetics model. Three macroscopic aspects of natural gas hydrate kinetic inhibition are also reported:  (1) The effect of hydrate dissociation residual structures was measured, which has application in decreasing the time required for subsequent formation. (2) The performance of a kinetic inhibitor (poly(N-vinylcaprolactam) or PVCap) was measured and correlated as a function of PVCap molecular weight and concentrations of PVCap, methanol, and salt in the aqueous phase. (3) Long-duration test results indicated that the use of PVCap can prevent pipeline blockage for a time exceeding the aqueous phase residence time in some gas pipelines.

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