Anion Photoelectron Spectroscopy and First-Principles Study of PbxIny Clusters*

Anionic and neutral Pb$_{x}$In$_{y}$ clusters containing up to 5 Pb and up to 7 In atoms have been investigated using negative ion photodetachment spectroscopy along with first-principles electronic structure studies within a gradient corrected density functional approach. The stability and electronic properties of these clusters have been characterized through studies of the detachment energies, gaps in the electronic spectrum, variations in binding energy, and nature of the electronic states. Particularly stable clusters have been grouped into two families of stable species. PbIn$_{3}^{-}$, Pb$_{2}$In$_{2}$, and Pb$_{3}$In$_{2}$ exhibit enhanced stability compared to their neighbors and the stability is linked to the aromatic character identified in their molecular orbitals. On the other hand, PbIn$_{5}^{-}$ and Pb$_{2}$In$_{4}$ exhibit enhanced stability associated with filled electronic shells within a confined nearly free electron gas.