Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey

TL;DR

This paper reports the first detection of ortho-benzyne (o-C6H4) in space within TMC-1, providing insights into hydrocarbon chemistry and formation pathways in interstellar environments.

Contribution

It is the first identification of o-C6H4 in space, expanding knowledge of interstellar hydrocarbons and their formation mechanisms.

Findings

Detected o-C6H4 with a column density of (5 +/- 1)e11 cm-2

o-C6H4 abundance is about 30 times lower than cyclopentadiene and indene

Proposed formation pathways include reactions of radicals like C2H, C, and C3H with hydrocarbons

Abstract

We report the detection, for the first time in space, of a new non-functionalised hydrocarbon cycle in the direction of TMC-1: o-C6H4 (ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5 +/- 1)e11 cm-2. The abundance of this species is around 30 times lower than that of cyclopentadiene and indene. We compare the abundance of benzyne with that of other pure hydrocarbons, cycles or chains, and find that it could be formed from neutral-radical reactions such as C2H + CH2CHCCH and C + C5H5, and possibly through C4H + C2H4, C3H + CH2CCH2, and C3H2 + C3H3. Hence, the rich content of hydrocarbon cycles observed in TMC-1 could arise through a bottom-up scenario involving reactions of a few radicals with the abundant hydrocarbons recently revealed by the QUIJOTE line survey.