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

Carbon-doped aluminum cluster anions, Al n C - ( n = 6-15), were generated by laser vaporization and investigated by mass-selected anion photoelectron spectroscopy. The geometric structures of Al n C - ( n = 6-15) anions were determined by the comparison of theoretical calculations with the experimental results. It is found that the most stable structure of Al 6 C - is a carbon endohedral triangular prism. The Al 7 C - anion is a magic cluster with high stability. The structures of Al 7-9 C - can be viewed as the additional aluminum atoms attached around the triangular prism Al 6 C - . Two isomers of Al 10 C - have been detected in the experiments. The most stable one has a planar tetracoordinate carbon structure. The second one derives from Al 9 C - with the carbon atom located in a pentagonal bipyramid. The Al 11 C - 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 Al 12-14 C - can be viewed as evolving from Al 11 C - by adding aluminum atoms to interact with the carbon atom. In Al 15 C - , the carbon atom stays at the surface with a tetracoordinate structure, and an icosahedral Al 13 unit can be identified as a part of the geometric structure of Al 15 C - .