Surface and Bulk Diffusion on Single-Crystal Ice and Acid Hydrate Multilayers

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The investigation of the diffusion of small, atmospherically relevant molecules on and in ice is the subject of this research project supported jointly by the Analytical and Surface Chemistry Program and the Atmospheric Chemistry Program. Laser resonant desorption methods will be used to probe the diffusion of ClONO2, HOCl, HNO3 and HCl on the surface and in the bulk of ice and acid hydrate multilayers produced and characterized in an ultra high vacuum apparatus. An understanding of the diffusion process and a knowledge of diffusion rates is important to developing an understanding of the heterogeneous chemistry of polar stratospheric clouds that convert stable halogen containing reservoir molecules into active halogen species which destroy ozone catalytically in the stratosphere. This work will also provide new basic information about the diffusion process on and in molecular solids. In order to understand the detailed mechanisms and rates of stratospheric ozone depletion by man made chemicals such as chlorofluorocarbon propellants and refrigerants, it is important to know about the rates and mechanisms of diffusion of these molecules and their decomposition products on the surfaces and in the bulk of the ice particles which exist in the stratosphere. Obtaining this understanding is the goal of this research project. Using laser desorption methods developed previously by the principal investigator, the details of this diffusion process will be examined. This information will help in developing models of the chemistry of the atmosphere which will aid scientists in proposing solutions for problems such as the depletion of the ozone layer in the stratosphere.