s-p hybridization and electron shell structures in aluminum clusters: A photoelectron spectroscopy study

Using photoelectron spectroscopy of size-selected Al-x(-) (x = 1-162) clusters, we studied the electronic structure evolution of Al, and observed that the Al 3s- and 3p-derived bands evolve and broaden with cluster size and begin to overlap at Al-9. Direct spectroscopic signatures were obtained for electron shell structures with spherical shell closings at Al-11(-), Al-13(-), Al-19(-), Al-23(-), Al-35(-), Al-37(-), Al-46. Al-52, Al-55(-), Al-56, Al-66, and Al-73(-) The electron shell effect diminishes above Al-75 and new spectral features appearing in Al-x(-) (x > 100) suggest a possible geometrical packing effect in large clusters.