A comparative MRD-CI study of the electronic spectrum of linear and cyclic C 8+ clusters

Abstract

Multi-reference configuration interaction MRD-CI calculations are performed to compute the vertical electronic spectrum of linear and cyclic C 8 + clusters. The electronic spectrum of the linear C 8 + isomer is dominated by the transition 2 Π u←X 2 Π g computed at 5.45 eV. The first dipole-allowed transition of linear C 8 + ( 2 Δ u←X 2 Π g ) is calculated at 1.69 eV, whereas several transitions are calculated with medium oscillator strengths between 2.30 and 5.14 eV. For the cyclic C 8 + form we computed important transitions at 1.83 and 4.20 eV. In addition, the first dipole-allowed transition of cyclic isomer is computed at 0.77 eV ( 1 2B g←X 2B u ). This transition should help to identify the cyclic C 8 + species since there are no dipole-allowed transitions of the linear isomer in this energy region.