Combined Experimental and Theoretical Study of Al n X (n = 1−6; X = As, Sb) Clusters: Evidence of Aromaticity and the Jellium Model

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2010-02, Vol.114 (5), p.2045-2052
• Main Authors: Melko, Joshua J, Clayborne, Peneé A, Jones, Charles E, Reveles, J. Ulises, Gupta, Ujjwal, Khanna, Shiv N, Castleman, A. W
• Format: Article
• Language: English
• Subjects: A: Dynamics, Clusters, Excited States
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp908406h

The electronic structure of Al n X (n = 1−6; X = As, Sb) clusters has been investigated using a synergistic approach combining negative ion photoelectron spectroscopy and first principles electronic structure calculations. It is shown that Al3X and Al5X exhibit enhanced energetic stability, as evidenced from calculated removal and embedding energies as well as chemical stability manifested through a large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). However, the stabilities of these species are derived from different mechanisms. Al3As and Al3Sb, with HOMO−LUMO gaps of 1.86 and 1.73 eV, respectively, are shown to have planar geometries where the p orbitals combine to form one π and two σ aromatic orbitals reminiscent of conventional all-metal aromatic species. Al5As and Al5Sb, with 20 valence electrons, possess a closed electronic shell (1s2, 1p6, 1d10, 2s2) within a jellium framework and have HOMO−LUMO gaps of 1.12 and 1.17 eV, respectively.