2021A&A...652L...9C

We report the detection, for the first time in space, of a new non-functionalised hydrocarbon cycle in the direction of TMC-1: o-C₆H₄ (ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5.0±1.0)x10¹¹cm^–2. The abundance of this species is around 30 times lower than that of cyclopentadiene and indene. We compare the abundance of benzyne with that of other pure hydrocarbons, cycles or chains, and find that it could be formed from neutral-radical reactions such as C₂H + CH₂CHCCH and C + C₅H₅, and possibly through C₄H + C₂H₄, C₃H + CH₂CCH₂, and C₃H₂ + C₃H₃. Hence, the rich content of hydrocarbon cycles observed in TMC-1 could arise through a bottom-up scenario involving reactions of a few radicals with the abundant hydrocarbons recently revealed by the QUIJOTE line survey.