Chemical shifts and cluster structure

The 2p core-level electron binding energies of size-selected silicon cluster ions have been determined from soft x-ray photoionization efficiency curves. Local chemical shifts and global charging energy contributions to the 2p binding energy can be separated, because core-level and valence-band electron binding energies exhibit the same inverse radius dependence. The experimental 2p binding energy distributions show characteristic size-specific patterns that are well reproduced by the corresponding electronic density of states obtained from density functional theory modeling. These results demonstrate that 2p binding energies in silicon clusters are dominated by initial state effects, i.e., by the interaction with the local valence electron density, and can thus be used to corroborate structural assignments

Higher Ionization Energies from Sequential Vacuum Ultraviolet Multiphoton Ionization of Size Selected Silicon Cluster Cations

The second to fifth ionization energies and the appearance sizes of the higher charge states of silicon clusters with 6 92 atoms are determined by sequential vacuum ultraviolet multiphoton ionization of size selected cluster ions in a cryogenic ion trap. The higher ionization energies are well described by the charging energy in a spherical droplet model. In contrast to the electron affinity and the first ionization energy of silicon clusters, the higher ionization energies seem to change less abruptly at the prolate to spherical shape transitio