The electronic spectrum of C11 in its linear and cyclic conformation

Abstract

Large-scale multi-reference configuration interaction calculations are employed to differentiate in the electronic spectrum between the linear and cyclic isomers of C₁₁ by certain fingerprints. The ¹Σ_u⁺←X¹Σ_g⁺ transition of the linear isomer is calculated at 4.02 eV in reasonable agreement with the recently measured 3.69 eV in a neon matrix. The yet to be observed ¹Π_u←X¹Σ_g⁺ transition is computed at 2.13 eV. The spectrum of cyclic C₁₁ is characterized by three strong transitions calculated at 3.94 eV (3¹B₂), 4.03 eV (3¹A₁) and 4.59 eV (4¹B₂). In addition the first transition of cyclic C₁₁ occurs at 1.04 eV (1¹B₁←X¹A₁) but this transition is energetically close to the dipole-forbidden ¹Δ_u state of the linear isomer to which transitions become allowed in cis-bending displacements.