Structural and bonding properties of Ta2Cn-/0 (n=1-7) clusters: Size-selected anion photoelectron spectroscopy and theoretical calculations

The structures and chemical bond evolution of ditantalum doped carbon clusters Ta2Cn-/0 (n = 1-7) were studied via size-selected anion photoelectron spectroscopy and theoretical calculations. It is found that Ta2C-/0 has a triangular structure and Ta2C2-/0 has a quasi-rhombus structure with C-2v symmetry. Ta2C3- has a quasi-planar structure with a carbon atom and a C-2 unit interacting with two tantalum atoms, and the lowest-energy isomer of neutral Ta2C3 has a triangular bipyramid structure with three carbon atoms around the Ta-2 unit. Ta2C4-/0 has two C-2 units connected with the Ta-2 unit in parallel. Two isomers of Ta2C5- are observed, where both isomers have one carbon atom and two C-2 units bound to the Ta-2 unit in different ways. The most stable structure of neutral Ta2C5 has one carbon atom added on top of the Ta2C4 cluster. The most stable structures of Ta2C6-7-/0 can be viewed as a C-2 unit and a C-3 unit capping a butterfly like Ta2C4 structure, respectively. Molecular orbital analysis shows that neutral Ta2C3 has a large gap between its highest occupied molecular orbital and lowest unoccupied molecular orbital. Chemical bonding analysis reveals that the Ta-Ta interactions in Ta2Cn-/0 (n = 1-7) clusters are slightly weaker than the Ta-Ta interaction in bare Ta-2 due to the participation in forming multicenter bonds.