Spectroscopic evidence for the tricapped trigonal prism structure of semiconductor clusters

We have obtained photoelectron spectra (PES) for silicon cluster anions with up to 20 atoms. Efficient cooling of species in the source has allowed us to resolve multiple features in the PES fur all sizes studied. Spectra for an extensive set of low-energy Si-n(-) isomers found by a global search have been simulated using density functional theory and pseudopotentials. Except for n = 12, calculations for Si-n(-) ground states agree with the measurements. This does not hold for other plausible geometries, Hence PES data validate the tricapped trigonal prism morphologies for medium-sized Si clusters.