Theoretical studies on the electronic spectrum of linear C6 Original Research Article

Large-scale multireference configuration interaction calculations were performed on singlet and triplet states of linear cumulenic C6 in the range up to 6 eV. Vertical excitation energies ΔE and oscillator strengths f are reported. For the 13Σ−u←X3Σ−g system, whose most intense band is observed at 2.68 eV, ΔE (vertical)=2.66 was calculated, with f=0.023. A very strong 21Σ−u–X3Σ−g transition is calculated around 5.7 eV; a transition 3Π–X3Σ−g slightly below 5 eV should also be observable. The lowest singlet state, 11Δg, lies only 0.17 eV above X3Σ−g. Singlet states with large oscillator strengths (relative to 1Δg) are 11Δu at 3.15 eV, 1Πu and 1Φu states between 4 and 5 eV.