Photoelectron spectroscopy and ab initio study of boron-carbon mixed clusters: CB9- and C2B8-.

We performed a joint photoelectron spectroscopy and ab initio study of two carbon-doped boron clusters, CB(9)(-) and C(2)B(8)(-). Unbiased computational searches revealed similar global minimum structures for both clusters. The comparison of the experimentally observed and theoretically calculated vertical detachment energies revealed that only the global minimum structure is responsible for the experimental spectra of CB(9)(-), whereas the two lowest-lying isomers of C(2)B(8)(-) contribute to the experimental spectra. The planar "distorted wheel" type structures with a single inner boron atom found for CB(9)(-) and C(2)B(8)(-) are different from the quasi-planar structure of B(10)(-), which consists of two inner atoms and eight peripheral boron atoms. The adaptive natural density partitioning chemical bonding analysis revealed that CB(9)(-) and C(2)B(8) clusters exhibit π aromaticity and σ antiaromaticity, which is consistent with their planar distorted structures.