Scattering of small molecules at surfaces

Abstract

The interaction of energetic molecules with surfaces is of interest for nuclear fusion experiments, for the erosion of space vehicles, and for the understanding of basic charge exchange phenomena between metal surfaces and molecules. For the latter reason experiments with hyperthermal molecules are also of interest for catalytic processes and for the functioning of solid state sensors. In many cases the interaction of molecules with surfaces is governed by charge exchange processes. An obvious case is the catalytic oxidation of CO at surfaces where a negative carbon dioxide species is identified as an intermediate of the reaction. Negative carbon dioxide species are also found in beam experiments. Their yield and the correlated dissociation probabilities show the expected dependencies on e.g. the coverage of the metal with alkali metal layers. In the case of hydrogen molecules the influence of alkali layers is quite different. In chemisorption experiments alkalis cause a decrease of the dissociative chemisorption of hydrogen. In our beam experiments an increase of the molecular survival with alkali coverage is found accordingly. The interpretation of the findings gives more detailed insight into the dissociation mechanisms of small molecules.