Ab initio characterization of C(6).

Structural and spectroscopy parameters of C(6) are determined with ab initio calculations confirming the existence of nine isomers. Those geometries with high stability (the linear, where the electronic ground state is a triplet (X(3)Sigma(g)(-)), and the slightly distorted cyclic singlet (X(1)A(1)')) are determined with CASPT2/CASSCF. The effect of the correlation energy on the isomer stability is discussed. The local potential energy surfaces of the first electronic states of linear-C(6) are determined with CASPT2/CASSCF calculations and the ANO-L C[4s3p2d1f] basis set. We provide minimum energy geometries and excitation energies for 19 electronic states. A new assignment of the electronic spectrum transitions involving high-energy symmetry states is proposed. Electron affinity and ionization potential have been computed to be EA = 3.97 eV and IP = 9.73 eV.