Discovery of interstellar 3-cyano propargyl radical, CH2CCCN

TL;DR

This paper reports the first interstellar detection of the 3-cyano propargyl radical (CH2C3N) in TMC-1, analyzing its abundance, formation pathways, and implications for organic molecule synthesis in space.

Contribution

It presents the first detection of CH2C3N in space, details its observed properties, and explores its formation mechanisms and potential role in organic chemistry in the interstellar medium.

Findings

CH2C3N detected with a column density of (1.6 +/- 0.4)e11 cm-2

Ortho/para ratio of 2.4 +/- 1.2 suggests specific formation conditions

CH2C3N abundance is about 0.1 times that of CH3C3N, indicating different chemistry from smaller analogues.

Abstract

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)e11 cm-2 and an ortho/para ratio of 2.4 +/- 1.2, which implies an abundance ratio CH2C3N/CH3C3N around 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.