Structure, spectra, and mobility of low-pressure ices: Ice I, amorphous solid water, and clathrate hydrates at T < 150 K


  • J. Paul Devlin


Recent advances in the study of low-pressure water ices, including clathrate hydrates, are examined, highlighting aspects of modern science possibly related to the behavior of water ices in extraterrestrial environments. An effort has been made to identify properties of ice that are likely to be important in the conditions that exist in such environments and to review advances in understanding these properties. The basic science of crystalline ice I is relatively mature, but attention is given to concepts, such as point defects, which continue to evolve and which relate in an important manner to the low-temperature behavior of ice I as well as of amorphous ice and the clathrate hydrates. A concept of amorphous and microporous amorphous ice, developed in the early 1980s, is presented, but more recent characterizations are emphasized. Similarly, fundamental properties of clathrate hydrates are summarized and used in discussions of more recently appreciated characteristics that may be important in space science. Particular emphasis is placed on the formation, infrared spectroscopy, and behavior of clathrate hydrates in vacuo at temperatures below 150 K. The review closes with a section on the properties of ice nanoparticles, which have only recently emerged as a subject of molecular science. Modern experimental and theoretical studies of ice particles have focused on the infrared spectra and structure of the ice surface, and the interaction of the surface with molecular adsorbates. Since, with the exception of high-energy radiation, ice normally interacts with its environment through surface processes, such research may enlighten future studies.