Non-thermal Surface Chemistry of Halogenated Molecules: Giant Electron-induced Enhancements of Negative Ion Desorption

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Investigation of the mechanism of fluorine and chlorine anion emission from adsorbed layers of halogenated hydrocarbons irradiated by electrons forms the focus of this research project supported by the Analytical and Surface Chemistry Program. Professor Theodore Madey and his coworkers at Rutgers University are examining the enhanced emission of Cl- and F- from physisorbed layers of CFC's in contact with water, ammonia, or non-polar co-adsorbates. A series of measurements is being carried out to elucidate the mechanism of this enhanced emission, and the connection this may have to the heterogeneous chemistry of ozone in the stratosphere. Electron stimulated ion angular and energy distributions are measured under a variety of conditions of surface temperature, co-adsorbate polarity, and incident electron energy in order to provide mechanistic understanding of the fundamental surface processes of ion emission.When adsorbed layers of chlorofluorocarbon compounds are irradiated with low energy electrons, significant amounts of chlorine and fluorine anions are desorbed. In the presence of certain polar co-adsorbates such as water and ammonia, this emission is dramatically enhanced. This research project examines this effect with a series of ion angular and energy distribution measurements. Connections of this effect with problems of ozone depletion in heterogeneous stratospheric chemistry are made in this research. The results of these studies, in addition to providing considerable fundamental insight into ion processes at surfaces, may help to understand stratospheric ozone depletion processes