INFRARED-SPECTRA OF LARGE CLUSTERS CONTAINING SMALL ETHER MOLECULES - LIQUID, CRYSTALLINE, AND CLATHRATE-HYDRATE CLUSTER SPECTRA

Large clusters of different structural phases containing the small-ring ether molecules tetrahydrofuran, trimethylene oxide, and ethylene oxide have been prepared and studied spectroscopically using a simple cluster cell based on a small infrared gas cell. Pure ether clusters are formed efficiently upon loading of the precooled cell (80-130 K) to pressures of a few hundred Torr with a gaseous mixture of an ether diluted with N2. For the right choice of temperature the pure ether clusters, which tend to be exceptionally large, initially assume a supercooled liquid structure but convert to the stable crystal structure over the observation time of a few minutes. Approximate nucleation temperatures, for this phase transition, range from 125 K for tetrahydrofuran to 100 K for ethylene oxide. The crystalline-cluster absorption bands, for the ether vibrational modes having large oscillator strengths, are distorted by dominance of the longitudinal mode absorption as expected for ultrathin particles. When water is included as a third component of the gaseous mixture, with a concentration chosen to give cluster compositions appropriate to the respective clathrate hydrate structures, the clusters assume the crystalline clathrate hydrate structures for temperatures close to the optimum values for thin-film clathrate hydrate formation by vapor cocondensation methods. © 1990 American Institute of Physics.