Electronic Structure of Bi$_{3}$Ga$_{y}^-$ Semiconductor Clusters and the Special Stability of Bi$_{3}$Ga$_{2}^{-}$ - A Gas Phase Zintl Analogue

Here we present evidence that the gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap) can be tuned (1.12eV-1.89eV) by changing the Ga composition of Bi$_{3}$Ga$_{y}$ neutral and anionic clusters, some of which display special stability. Collaboratively, mass spectrometry, photoelectron spectroscopy and computational results show that Bi$_{3}$Ga$_{2}^{-}$ is a very stable cluster with a large calculated HOMO-LUMO gap of 1.89 eV, and can be viewed as a gas phase Zintl analogue of Sn$_{5}^{2-}$, already synthesized in the solution phase. The stability of Bi$_{3}$Ga$_{2}^{-}$ is further attributed to the fact that it has 12 valence electrons and possesses a closo structure in agreement with Wade's rules.