The C5N radical is found in both the envelopes of carbon stars (evolved stars whose atmospheres contain more carbon than oxygen, the excess carbon presumably produced by helium fusion in the latter stages of the star’s life) and in cold, dark interstellar molecular clouds (typically those that have not been heated by star formation). It is an intermediary in the chemistry of the cyanopolyynes and related molecules (Guelin et al. 1998). The rotational transitions of the cyanobutadiynyl radical are observed by radio astronomers at millimeter wavelengths. The anion of this species, C5N−, has also been found in space (Cernicharo et al. 2008).