A theoretical investigation of four electronic states of C6− and the ground state of linear C6

Large-scale open-shell coupled cluster calculations have been carried out for the four lowest doublet states of C6− and the ground state of linear C6. They strongly support the assignment of the peaks at 607.7 and 586.5 nm observed in neon matrix isolation experiments to the 000 and 301 transitions within the electronic band C̃ 2Πg ← X̃ 2Πu of C6−. The vibrational structure of the photoelectron spectrum of C6− has been calculated; the 101 transition is calculated to have 42% intensity with respect to the adiabatic peak. Some misassignments of the experimental threshold photodetachment and autodetachment spectra are corrected. Excellent agreement with experiment is obtained for the electron affinity of linear C6.