A high‐pressure optical cell was designed and fabricated for the measurement of hydrate phase equilibria. These measurements were carried out using Raman spectroscopy, which provided molecular microscopic evidence of hydrate dissociation, along with macroscopic temperature and pressure evidence. Initial measurements were made of hydrates formed from methane (CH4) dissolved in deionized water. Distinct signatures of CH4 in different phases (aqueous and sI hydrate) were the basis for this study. Time resolved Raman spectra monitored the dissociation of hydrate as cell temperature was increased. The spectra depicted the transition of CH4 in the two cavities of sI hydrate to CH4 dissolved in water. A pressure trace of the experiment indicated a slight jump in pressure of about 30 psi (0.2 MPa) at the hydrate dissociation point, which agreed with the Raman spectroscopic data. Experimental data obtained using this method agreed well with literature data for the simple methane system. The technique demonstrated that the optical cell is suitable for Raman measurements of hydrate phase equilibria at high pressures. Ultimately, this procedure will be used to measure thermodynamic conditions for more complex systems.

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Measurements are reported for the scattering of argon beams with energies between about 200-1500 eV by room-temperature argon, helium, and hydrogen. Two separate investigations in essentially the same apparatus are involved, and interaction potentials are derived for Ar-Ar and Ar-He at internuclear distances where scattering measurements have not previously been made. For Ar-H2 there are no previous direct scattering results. The Ar-Ar system was studied in both investigations, and the combined results are represented by V (r) =3.25X10 3 /r 9 . 97 eV,There is good agreement between this result and potentials from other scattering measurements and shock compression of liquid argon. One series of new measurements was made for Ar-He. The derived potential iswhich agrees well with other scattering results and with measurements of mutual diffusion coefficients at elevated temperatures. A combination of He-He potentials obtained from scattering with the present Ar-Ar results leads to a derived He-Ar potential which is in good agreement with that obtained from the direct measurements. One series of measurements was made for Ar-H2, and the resulting potential is, which is about a factor of 2 higher than that derived from previous measurements on He-He, He-H2, and Ar-Ar. It is also higher by about the same amount than the Ar-H2 potential derived from other scattering measurements on Ar-Ar and H2-H2. Mutual diffusion coefJicients for Ar-H2 at elevated temperatures also suggest that this potential is high. The present potential for Ar-Ar agrees well with theoretical calculations based on a delta-function model and a statistical (Thomas-Fermi-Dirac) model. The Ar-He potential also agrees with calculated potentials based on these models and with that obtained from ab initio Hartree-Fock calculations.

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