Structural Evolution of Carbon-Doped Aluminum Clusters AlC ( = 6-15): Anion Photoelectron Spectroscopy and Theoretical Calculations.

Carbon-doped aluminum cluster anions, AlC ( = 6-15), were generated by laser vaporization and investigated by mass-selected anion photoelectron spectroscopy. The geometric structures of AlC ( = 6-15) anions were determined by the comparison of theoretical calculations with the experimental results. It is found that the most stable structure of AlC is a carbon endohedral triangular prism. The AlC anion is a magic cluster with high stability. The structures of AlC can be viewed as the additional aluminum atoms attached around the triangular prism AlC. Two isomers of AlC have been detected in the experiments. The most stable one has a planar tetracoordinate carbon structure. The second one derives from AlC with the carbon atom located in a pentagonal bipyramid. The AlC anion has a bilayer structure composed of one planar tetracoordinate carbon and one aluminum-centered hexagon, in which the major interactions between two layers are multicenter bonds. The structures of AlC can be viewed as evolving from AlC by adding aluminum atoms to interact with the carbon atom. In AlC, the carbon atom stays at the surface with a tetracoordinate structure, and an icosahedral Al unit can be identified as a part of the geometric structure of AlC.