Spectroscopic evidence for the tricapped trigonal prism structure of semiconductor clusters

We have obtained photoelectron spectra (PES) for silicon cluster anions wit h 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 ha ve been simulated using density functional theory and pseudopotentials. Exc ept for n = 12, calculations for Si-n(-) ground states agree with the measu rements. This does not hold for other plausible geometries, Hence PES data validate the tricapped trigonal prism morphologies for medium-sized Si clus ters.