The electronic structure and chemical bonding of aluminum acetylide:Al_2C_2 and Al_2C_2~-:An experimental and theoretical investigation

摘要

We have investigated the electronic structure and chemical bonding of Al_2C_2 and Al_2C_2 both experimentally and theroetically. Photoelctron spectra of Al_2C_2~- 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 bindinng energy (1.58 eV). Theoretical calculations wer 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 quasiliner acetylide species and a planar-bridged D_(2h) structure. However,only one stable isomer was found for theneutral, which has the acetylide structure. Adiabatic and vertical detachment energies were also calculated for the two anionic isomers and were used to ijterpret 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 o fthe acetylide neutral and anion and the D_(2h) anion are discussed.