2021A&A...654L...9C

We report the first detection in interstellar space of the 3-cyano propargyl radical (CH₂C₃N). This species was observed in the cold dark cloud TMC-1 using the Yebes 40m telescope. A total of seven rotational transitions for both ortho- and para-CH₂C₃N species were observed in the 31.0-50.4 GHz range. We derive a total column density of (1.6±0.4) x 10¹¹ cm^–2 and an ortho/para ratio of 2.4±1.2, which implies an abundance ratio CH₂C₃N/CH₃C₃N∼0.1, in sharp contrast with the smaller analogues, in which case CH₂CN/CH₃CN∼3. This indicates that the chemistry of the cyanides CH₂C₃N and CH₃C₃N behaves differently to that of the smaller analogues CH₂CN and CH₃CN. According to our chemical model calculations, the radical CH₂C₃N is mostly formed through the neutral-neutral reactions C + CH₂CHCN, C₂ + CH₃CN, and CN + CH₂CCH together with the dissociative recombination of the CH₃C₃NH⁺ ion with electrons. The neutral-neutral reaction N + C₄H₃ could also lead to CH₂C₃N, although its role is highly uncertain. The identified radical CH₂C₃N could play a role in the synthesis of large organic N-bearing molecules, such as benzonitrile (c-C₆H₅CN) or nitrogen heterocycles.