The electronic structure and chemical bonding of aluminum acetylide:: Al2C2 and Al2C2-:: An experimental and theoretical investigation

We have investigated the electronic structure and chemical bonding of Al2C2 and Al2C2- both experimentally and theoretically. Photoelectron spectra of Al2C2- were obtained at several photon energies. Two anionic isomers were observed: one with a very sharp ground state feature and a low vertical electron binding energy (0.71 eV) and another with a very broad ground state feature with a much higher vertical electron binding energy (1.58 eV). Theoretical calculations were performed at various levels of theory for both the anion and the neutral. We found two isomers with relatively close energies for the anion: a quasilinear acetylide species and a planar-bridged D-2h structure. However, only one stable isomer was found for the neutral, which has the acetylide structure. Adiabatic and vertical detachment energies were also calculated for the two anionic isomers and were used to interpret and assign the experimental spectra. We found that the sharp 0.71 eV feature was from the acetylide isomer, whereas the broad 1.58 eV feature was from the D-2h isomer. The excellent agreement between the calculated and experimental electron affinities and excitation energies lends considerable credence for the assignments of the two anionic isomers. The structures and bonding of the acetylide neutral and anion and the D-2h anion are discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)30831-5].