SCATTERING OF SMALL MOLECULES AT SURFACES

The interaction of energetic molecules with surfaces is of interest fo r nuclear fusion experiments, for the erosion of space vehicles, and f or the understanding of basic charge exchange phenomena between metal surfaces and molecules. For the latter reason experiments with hyperth ermal molecules are also of interest for catalytic processes and for t he functioning of solid state sensors. In many cases the interaction o f molecules with surfaces is governed by charge exchange processes. An obvious case is the catalytic oxidation of CO at surfaces where a neg ative carbon dioxide species is identified as an intermediate of the r eaction. Negative carbon dioxide species are also found in beam experi ments. Their yield and the correlated dissociation probabilities show the expected dependencies on e.g. the coverage of the metal with alkal i metal layers. In the case of hydrogen molecules the influence of alk ali layers is quite different. In chemisorption experiments alkalis ca use a decrease of the dissociative chemisorption of hydrogen. In our b eam experiments an increase of the molecular survival with alkali cove rage is found accordingly. The interpretation of the findings gives mo re detailed insight into the dissociation mechanisms of small molecule s.