Gas phase electronic spectra of carbon chains Cn (n=6-9)

Ultraviolet electronic transitions of the linear carbon chains C6, C7, C8, and C9 were measured in the gas phase by a mass-resolved 1 + 1 resonant two-photon ionization technique using a picosecond laser. Broad absorptions with band maxima at 230.2 and 259.0 nm are identified as N3Σ−u − X3Σ−g (N < 3) transition of C6 and C8, respectively. Based on calculated Franck-Condon intensities, the band maxima are identified as origin bands. An upper limit of 30 ps is determined for the N3Σ−u excited state lifetime of C6. The 1Σ+u − X1Σ+g transition with band maximum at 238.5 nm was observed for C7 and at 279.0 nm for C9. The proposition that intramolecular processes in the excited electronic states of carbon chains can lead to broadening as in the diffuse interstellar absorptions is experimentally demonstrated.