Theoretical characterization of C7, C7-, and C7+

We present a theoretical investigation of neutral and ionic C-7 molecules. Since carbon chains present isomerism and the number of possible structures increases fast with the number of carbon atoms, a B3LYP/aug-cc-pVTZ search of stationary points has been achieved. For C-7, we found twelve minimal structures. Among these forms, eleven C-7 isomers are located into the lowest singlet hyper potential energy surface. The most stable form of C-7 is linear and possesses a (1)Sigma(+)(g) symmetry species. For C-7(-), we characterized fifteen stable forms, where twelve are of doublet spin-multiplicity. The global minimum of C-7(-) is a (2)Pi(g) doubly degenerate Renner-Teller structure. For C-7(+) cation, we found eleven doublet and three quartet isomers with a 7-atom cycle, C-7(+) (X(2)A(1)) ground state. For the most stable forms, explicitly correlated (R)CCSD(T)-F12 calculations have been performed for the determination of equilibrium geometries and for the spectroscopic characterization of C-7, C-7(-), and C-7(+), providing accurate rotational constants and harmonic frequencies. Vertical excitation energies to the lowest electronic states have been computed at the CASSCF/MRCI/aug-cc-pVTZ level. Thirty five electronic states of C-7, suitable of being involved in reactive processes, lie below 7 eV. Fourteen metastable electronic states of C-7(-) have been found below 3.5 eV. For linear-C-7, we compute the electron affinity and the ionization energy to be 3.38 eV and 10.42 eV, respectively. (C) 2013 AIP Publishing LLC.