Coupled cluster calculations for linear C8−(X̃ 2Πg and C̃ 2Πu) and C8 (X̃ 3Σg−)

Large-scale open-shell coupled cluster calculations have been carried out for the two lowest 2Π states of C8− and the electronic ground state of linear C8. The calculated spectrum of the 2Πu ← X̃ 2Πg transition is in good agreement with the recent neon matrix absorption spectrum of Freivogel, Fulara, Jacobi and Maier. The calculated adiabatic electron affinity of C8 is 4.348 eV, in close agreement with the experimental value of 4.379 ± 0.006 eV. The 4.66 eV photoelectron spectrum of C8− is dominated by the adiabatic peak; the 101 and 301 transitions have relative intensities of 24% and 13%, respectively.