In this project in the Physical Chemistry program of the Chemistry Division, Prof. M. Jarrold of Northwestern University will study the structure and chemistry of gas phase atomic clusters. Geometric structures, structural isomers, and structural transitions will be determined with an improved ion-chromatography technique. Additionally, information will be obtained on previously inaccessible features such as cluster annealing and the temperature at which clusters isomerize and undergo a phase transition. Thermal desorption measurements on clusters will be used to unravel the chemistry that occurs on the nano-surfaces of atomic clusters, and to determine accurate dissociation energies and ligand binding energies. Specific cluster systems to be studied will include large fullerene-type carbon clusters composed of more than 100 carbon atoms and semiconductor clusters. %%% Clusters of atoms (and molecules) constitute a form of aggregated matter that bridges the traditional conceptual boundary between the condensed (solid or liquid) and gaseous states of aggregation. Because the physical and chemical properties of clusters differ from those of the condensed or gaseous phases of the concerned material, the study of cluster properties is of fundamental interest. In addition to the exploration of cluster properties for their intrinsic interest, there is strong coupling to the technological applications of clusters. Fullerenes, or buckyballs, are clusters in which the constituent atoms arrange themselves to form three dimensional geodesic structures. The appellation fullerene (or buckyball) is given to this type of cluster in recognition of Buckminster Fuller who is known for his designs of geodesic domes. Fullerenes are now recognized to constitute a new, third form of carbon in addition to the well known forms graphite and diamond. Their physical and chemical properties are intensively investigated to increase our knowledge about them and to exploit it for technological applications.