Comparative sulfur dioxide infrared spectra: type I and II clathrate hydrate films, large gas-phase clusters, and anhydrous crystalline films

Abstract

The mechanism by which SO{sub 2} is incorporated into microparticles of ice in the vapor phase is receiving special interest because of the unexpectedly high efficiency with which SO{sub 2} is scavenged by ice crystals. A possible explanation of this efficiency might be found in the tendency for small polar molecules, such as the small ring ethers, to form clathrate hydrates at low temperatures and low partial pressures. This possibility has been examined by spectroscopic studies at {approximately} 120 K of large gas-phase clusters formed from anhydrous SO{sub 2} and H{sub 2}O-SO{sub 2} mixtures with a ratio appropriate for clathrate hydrate formation. On the basis of a comparison with new thin-film infrared data for the simple type I SO{sub 2} hydrate, the mixed SO{sub 2}-ethylene oxide type I hydrate and the type II double hydrate with tetrahydrofuran, it is apparent that SO{sub 2} is not enclathrated under the conditions that are known to cause formation of clathrate hydrate crystalline clusters of ethylene oxide, trimethylene oxide, and tetrahydrofuran.