Discovery of interstellar 3-cyano propargyl radical, CH<sub>2</sub>CCCN
C. Cabezas, M. Agúndez, N. Marcelino, B. Tercero, J. R. Pardo, P. de Vicente, J. Cernicharo
Abstract
We report the first detection in interstellar space of the 3-cyano propargyl radical (CH 2 C 3 N). 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-CH 2 C 3 N species were observed in the 31.0–50.4 GHz range. We derive a total column density of (1.6 ± 0.4) × 10 11 cm −2 and an ortho/para ratio of 2.4 ± 1.2, which implies an abundance ratio CH 2 C 3 N/CH 3 C 3 N ∼ 0.1, in sharp contrast with the smaller analogues, in which case CH 2 CN/CH 3 CN ∼ 3. This indicates that the chemistry of the cyanides CH 2 C 3 N and CH 3 C 3 N behaves differently to that of the smaller analogues CH 2 CN and CH 3 CN. According to our chemical model calculations, the radical CH 2 C 3 N is mostly formed through the neutral-neutral reactions C + CH 2 CHCN, C 2 + CH 3 CN, and CN + CH 2 CCH together with the dissociative recombination of the CH 3 C 3 NH + ion with electrons. The neutral-neutral reaction N + C 4 H 3 could also lead to CH 2 C 3 N, although its role is highly uncertain. The identified radical CH 2 C 3 N could play a role in the synthesis of large organic N-bearing molecules, such as benzonitrile ( c –C 6 H 5 CN) or nitrogen heterocycles.