Gas-phase electronic spectra of carbon-chain radicals compared with diffuse interstellar band observations

This paper compares laboratory gas-phase spectra of neutral and cationic linear carbon-chain radicals with astronomical diffuse interstellar band (DIB) spectra. The origin bands of the strong electronic transitions of the studied species, C2nH (n = 3-6), HC2nH+ (n = 2-4), NC2n-2N+ (n = 3, 4), do not coincide with detectable DIBs, except for HC2n-1N+ (n = 3), which possibly matches a weak feature. It is concluded that the column densities of these species through the observed diffuse clouds are below 2 x 10(12) cm(-2). The profile change and the shift of the maxima of the absorption bands with temperature are illustrated. The relation to radio-astronomical detection of carbon chains in diffuse media is also discussed.