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The spectroscopic investigation of clathrate hydrates prepared by using low-temperature thin-film techniques has been extended to several new gases. These gases have included a highly polar gas (trimethylene oxide or TMO) the simple hydrate of which grows readily from a vapor beam at 120 K, a slightly less polar gas (methyl chloride) the simple hydrate of which grows if the vapor beam is incident onto a crystalline clathrate hydrate base at 125 K, and a nonpolar gas (carbon dioxide) which apparently can only be enclathrated as the mixed hydrate by using a highly polar help gas (e.g., ethylene oxide (EtO)). These structure I hydrates as well as the structure II hydrate of tetrahydrofuran have been prepared under conditions of temperature/ base-doping such that no mobile protons exist during the deposit. As a result, it has been possible to isolate intact D20 molecules in the water network of the crystalline hydrates. A comparison of the D20 spectrum of the TMO structure I hydrate with the corresponding published spectrum for the EtO hydrate shows vividly the influence of the larger TMO molecules on the host-lattice structure. The TMO data suggest that the D20 molecules divide sharply into two subsets differing in the relative lengths of the average of the two O-D--O hydrogen bonds of each isolated D20 molecule. An analysis of the distribution of bond lengths for a typical structure I hydrate shows that such a division is expected in any case, but is apparently enhanced by the host-guest interactions of TMO. The guest-molecule spectra, all obtained at 90 K, show (a) the apparent generality of the rule that guest-molecule stretching-mode frequencies decrease with an increase in cage size and (b) that the effective size of the structure I small cage increases as the size of the molecule occupying the large cage increases.

Isotherms have been measured at temperatures ranging from 0 to 150 °C for the adsorption of benzene, toluene, and p-xylene on silicalite. Results show that the shape of the isotherms changes from type I to type IV with decreasing temperature. This unusual behavior is consistent with a two-patch heterogeneous model with surface-phase transition. Although silicalite pore walls are homogeneous, "structural heterogeneity" results because the adsorbate molecules are comparable in size to channels in silicalite, thereby restricting the motion of the molecules in the surface phase. Isotherms have been modeled by considering that adsorption takes place on a high-energy patch and a low-energy patch. Local equilibria on both patches are described by the Hill-deBoer model. The heat of adsorption is found to go through a maximum as predicted by this model. The two-patch model is effective in correlating the adsorption isotherm for the three test gases. The simulations and data are also in agreement with results obtained by other researchers utilizing different experimental techniques.