How different are mechanisms of chemical reactions on atoms and clusters compared to their bulk analogs?

Whether one can learn something about the condensed phase from clusters strongly depends on the property under consideration. For a chem. reaction for instance subtle changes in the electronic and geometric structure when going from the atom to the bulk are detg. for the outcome of the reaction. In our exptl. studies on the chem. properties of cluster-assembled materials, metal atoms and small metal clusters are formed in the gas phase, size-selected and then deposited on thin MgO and TiO2 films grown on metal surfaces. Various chem. reactions on the obtained cluster-assembled materials are then investigated under UHV conditions by means of thermal desorption and IR spectroscopies. Oxidn. and polymn. reactions are strongly dependent on cluster size and on the cluster-support interaction, and not only the no. of product mols. per cluster is changed, but also the branching ratio of the certain reactions. In many cases the measured reactivities are different from the ones obtained for the corresponding bulk systems. In addn., first-principle calcns. are used for studying some of the chem. reactions on oxide supported metal clusters. Detailed reaction mechanisms are proposed, which describe many of the exptl. observations. Comparing the proposed reaction mechanisms with the ones for the bulk analogs can elucidate distinct differencies in the chem. behavior of clusters and condensed matter. [on SciFinder(R)]     «

Whether one can learn something about the condensed phase from clusters strongly depends on the property under consideration. For a chem. reaction for instance subtle changes in the electronic and geometric structure when going from the atom to the bulk are detg. for the outcome of the reaction. In our exptl. studies on the chem. properties of cluster-assembled materials, metal atoms and small metal clusters are formed in the gas phase, size-selected and then deposited on thin MgO and TiO2 films...     »