Discovery of the cyclic C5H radical in TMC-1

Abstract

Cyclic C5H (c-C5H), the radical formed by substituting an ethynyl group CCH for the hydrogen atom in the c-C3H radical, has been detected for the first time in the space. The c-C5H species is an isomer of the well-known linear radical l-C5H and is 6 kcal/mol less stable. A total of 17 rotational transitions were detected for the c-C5H species in TMC-1 within the 31.0-50.3 GHz range using the Yebes 40m radio telescope. We derive a column density of (9.0 +/- 0.9)e10 cm-2 for c-C5H. Additionally, we observed 12 lines for l-C5H and derive a column density for it of (1.3 +/- 0.3)e12 cm-2, which results in an abundance ratio c-C5H/l-C5H of 0.069. This is in sharp contrast with the value found for the analogue system c-C3H/l-C3H, whose ratio is 5.5 in TMC-1. We discuss the formation of c-C5H and conclude that this radical is probably formed in the reaction of atomic carbon with diacetylene.

Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor. The official date of acceptance is 31/05/2022

References in corpus (16)

• The 2014 KIDA network for interstellar chemistry
• Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• Yebes 40 m radio telescope and the broad band NANOCOSMOS receivers at 7 mm and 3 mm for line surveys
• The interstellar chemistry of C3H and C3H2 isomers
• Space and laboratory discovery of HC3S+
• Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1
• Tentative detection of HC5NH+ in TMC-1
• Discovery of the elusive thioketenylium, HCCS+, in TMC-1
• Discovery of the acetyl cation, CH3CO+, in space and in the laboratory
• Cumulene carbenes in TMC-1: Astronomical discovery of $l$-H${}_2$C${}_5$
• HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
• Discovery of C5H+ and detection of C3H+ in TMC-1 with the QUIJOTE line survey
• Discovery of a new molecular ion, HC7NH+, in TMC-1
• A new protonated molecule discovered in TMC-1: HCCNCH+
• A molecular line survey of the extreme carbon star CRL 3068 at millimeter wavelengths

Cited by in corpus (4)

• Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey
• Carbon-Chain Chemistry in the Interstellar Medium
• Laboratory and astronomical discovery of cyanothioketene, NCCHCS, in the cold starless core TMC-1
• Chemistry of Dark Molecular Clouds