Identification of the interstellar 1-cyano propargyl radical (HCCCHCN) in TMC-1

TL;DR

This paper reports the first detection of the interstellar 1-cyano propargyl radical in TMC-1, providing insights into its abundance, formation, and relation to isomers in cold dark clouds.

Contribution

It presents the first interstellar detection of HC3HCN, including measurements of its abundance, temperature, and potential formation pathways in TMC-1.

Findings

Detected seven rotational transitions of HC3HCN in TMC-1.

Derived a column density of (2.2±0.2)×10^11 cm^-2 and a rotational temperature of 7±1 K.

Found an abundance ratio of 1.4 between HC3HCN and its isomer CH2C3N.

Abstract

We report the first detection in interstellar medium of the 1-cyano propargyl radical, HC$_3$HCN. This species is an isomer of the 3-cyano propargyl radical (CH$_2$C$_3$N), which was recently discovered in TMC-1. The 1-cyano propargyl radical was observed in the cold dark cloud TMC-1 using data from the ongoing QUIJOTE line survey, which is being carried out with the Yebes 40m telescope. A total of seven rotational transitions with multiple hyperfine components were detected in the 31.0-50.4 GHz range. We derived a column density of (2.2$\pm$0.2)$\times$10$^{11}$ cm$^{-2}$ and a rotational temperature of 7$\pm$1\,K. The abundance ratio between HC$_3$HCN and CH$_2$C$_3$N is 1.4. The almost equal abundance of these isomers indicates that the two species may be produced in the same reaction with a similar efficiency, probably in the reaction C + CH$_2$CHCN and perhaps also in the reaction C$_2$ + CH$_3$CN and the dissociative recombination with electrons of CH$_2$C$_3$NH$^+$