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, C 2 n H ( n = 3-6), HC 2 n H + ( n = 2-4), NC 2 n -2 N + ( n = 3, 4), do not coincide with detectable DIBs, except for HC 2 n -1 N + ( 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 × 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.