On the Electronic Structure and Chemical Bonding in the Tantalum Trimer Cluster

The electronic structure and chemical bonding in the Ta-3(-) cluster are investigated using photoelectron spectroscopy and density functional theory calculations. Photoelectron spectra are obtained for Ta3- at four photon energies: 532, 355, 266, and 193 nm. While congested spectra are observed at high electron binding energies, several low-lying electronic transitions are well resolved and compared with the theoretical calculations. The electron affinity of Ta-3 is determined to be 1.35 +/- 0.03 eV. Extensive density functional calculations are performed at the B3LYP/Stuttgart +2f 1g level to locate the ground-state and low-lying isomers for Ta-3 and Ta-3(-). The ground-state for the Ta-3(-) anion is shown to be a quintet ((5)A(1)') with D-3h symmetry, whereas two nearly isoenergetic states, C-2v ((4)A(1)) and D-3h ((6)A(1)'), are found to compete for the ground-state for neutral Ta-3. A detailed molecular orbital analysis is performed to elucidate the chemical boding in Ta-3(-), which is found to possess multiple d-orbital aromaticity, commensurate with its highly symmetric D-3h structure.