Discovery of HCCCH2CCH in TMC-1 with the QUIJOTE line survey

TL;DR

This paper reports the first space detection of 1,4-pentadiyne in TMC-1, using radio astronomy data, and combines observational, computational, and chemical modeling to analyze its properties and formation pathways.

Contribution

It presents the first detection of 1,4-pentadiyne in space and provides detailed analysis of its abundance, energy, and formation mechanisms in TMC-1.

Findings

Detected 17 transitions of 1,4-pentadiyne in TMC-1

Derived rotational temperature of 9.5 K and column density of 5.0e12 cm^-2

Chemical modeling supports observed abundances and reaction pathways

Abstract

We present the first detection in space of 1,4-pentadiyne. It has been found towards TMC-1 with the QUIJOTE line survey in the 31-50 GHz range. We observed a total of 17 transitions with J = 2 up to 13 and Ka = 0, 1 and 2. The observed transitions allowed us to derive a rotational temperature of 9.5 +- 0.5 K and a column density of (5.0 +- 0.5) x 10^12 cm-2. This molecule was the last non-cyclic isomer of the C5H4 family that could be detected via radio astronomy. A computational chemistry study was performed to determine the energies of the five most stable isomers. The isomer (c-C3H3CCH) has a considerably higher energy than the others, and it has not yet been detected. To better understand the chemical reactions involving these species, we compared the ethynyl and cyano derivatives. The observed abundances of these species are in good agreement with the branching ratios of the formation reactions studied with our chemical model of TMC-1.