STRUCTURAL TRANSITIONS IN SIZE-SELECTED GERMANIUM CLUSTER IONS

Injected ion drift tube techniques have been used to probe the geometries of germanium cluster ions. Clusters with similar to(10-40) atoms appear to follow a one-dimensional growth sequence to give prolate geometries. At similar to 40 atoms the clusters stop following this growth sequence, and clusters with similar to(40-70) atoms appear to retain roughly the same aspect ratio. At similar to 70 atoms the clusters abruptly reconstruct to a more spherical geometry. Dissociation energies, measured for the germanium clusters, suggest that clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge-7 and Ge-10) It appears that the structural transition at similar to 70 atoms may reflect a change to a more bulklike bonding arrangement.