Under impact of 150-keV/atom ${\mathrm{Au}}_n^{+}$ projectiles $(1\mathrm{}<~n<~9)$ on gold targets the emission yield of anionic clusters increases much faster with $n$ than expected from simple proportionality. Moreover the anion size distribution is much wider for bombardment by clusters. The cluster yield enhancements reflect the size dependence of the cluster stability according to the electronic shell structure. Accordingly, the most intense emission is observed for ${\mathrm{Au}}_7^{-}:$ under ${\mathrm{Au}}_9^{+}$ impact the ${\mathrm{Au}}_7^{-}$ yield per incident atom is enhanced by a factor of $\sim 6.$

• Received 18 July 2003

DOI:https://doi.org/10.1103/PhysRevB.68.140102