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Clusters containing two to several hundred atoms are generated by pulsed laser vaporization of a metal target located in a flow tube reactor. A continuous flow of inert carrier gas entrains and cools the vaporized plume of metal, resulting in rapid cluster growth. Reactant gases are injected into the flow downstream of the target, at a point where cluster growth has finished. After reagent mixing and chemical reactions occur, the products exit the tube into a vacuum, and are formed into a molecular beam by collimators located in successive stages of differential pumping. In the highest vacuum stage the reaction products are identified by pulsed laser ionization and time-of-flight mass spectrometry. Studies to be discussed include measurements of absolute reaction rate constants, hydrogen uptake experiments, laser-induced desorption of adsorbates from clusters, and cluster-catalyzed chemical reactions. Such work provides us with information about the dependence of reactivity on cluster size, the geometrical configuration of cluster binding sites, the thermodynamics of adsorbate bonding, and the mechanisms of chemical reactions on cluster surfaces. These studies are bringing us closer to a detailed understanding of the interactions of metal surfaces with atoms and simple molecules.
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