Structural Transitions in Size-Selected Germanium Cluster Ions

Abstract

Injected ion drift tube techniques have been used to probe the geometries of germanium cluster ions. Clusters with \ensuremath{\sim}(10-40) atoms appear to follow a one-dimensional growth sequence to give prolate geometries. At \ensuremath{\sim}40 atoms the clusters stop following this growth sequence, and clusters with \ensuremath{\sim}(40-70) atoms appear to retain roughly the same aspect ratio. At \ensuremath{\sim}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 ${\mathrm{Ge}}_{7}$ and ${\mathrm{Ge}}_{10}$). It appears that the structural transition at \ensuremath{\sim}70 atoms may reflect a change to a more bulklike bonding arrangement.