Fast Ion Bombardment of Ices and Its Astrophysical Implications

Ices such as water, carbon dioxide, and methane are now known to be pervasive constituents of the solar system and probably of the interstellar medium as well. Many of these ices and ice-covered surfaces are exposed to bombardment by the energetic ions of space. Laboratory experiments have been carried out to study the effects of such bombardment. Surprisingly efficient erosion of ice layers is associated with electronic excitation of the ices by the ions. These results are a challenge to an understanding of the physical processes involved and have implications for a number of astrophysical problems of current interest.

Ion Beam Spectroscopy of Solids and Surfaces

Ion beams are important new probes for characterizing the chemistry and structure of a wide variety of materials. When beams of particles with energies of approximately 1000 electron volts are used, as in secondary ion mass spectrometry, it is possible to detect ions ejected from the top layer of the material with sensitivities we below the picogram level. A number of theoretical developments now permit analysis of the geometry of adsorbed atoms and molecules on surfaces from the angular distributions of the ejected particles. Much surface chemical information can also be deduced from ejected molecular cluster ions. In addition, the observation of clusters with weights up to nearly 20,000 atomic mass units promises to expand applications of mass spectrometry to the analysis of biomolecules and the sequencing of proteins.