Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: Abundances of CCH and CN derivatives of hydrocarbon cycles

Abstract

We report the detection of two isomers of ethynyl cyclopentadiene (c-C 5 H 5 CCH), namely 1-and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4±0.2)×10 12 cm −2 and (2.0±0.4)×10 12 cm −2 , respectively, for these two cyclopentadiene derivatives, which imply that they are about ten times less abundant than cyclopentadiene. We also report the tentative detection of ethynyl benzene (C 6 H 5 CCH), for which we estimate a column density of (2.5±0.4)×10 12 cm −2 . We derived abundances for the corresponding cyano derivatives of cyclopentadiene and benzene and found values significantly lower than previously reported. The rotational temperature of the ethynyl and cyano derivatives of these cycles is about 9 K, that is, very close to the gas kinetic temperature of the cloud. The abundance ratio of the 1-and 2-isomers of ethynyl cyclopentadiene is 1.4±0.5, while for the two isomers of cyano cyclopentadiene it is 2.4±0.6. The relative abundances of CCH over CN derivatives is 7.7±2.2 for cyclopentadiene, which probably reflects the abundance ratio of the radicals CCH and CN; this ratio is only 2.1±0.5 for benzene, which suggests that additional reactions besides cyano radicals with benzene are involved in the formation of benzonitrile. The formation of these cycles is reasonably well accounted for through a chemical scheme based on neutral-neutral reactions. It is predicted that benzene should be as abundant as cyclopentadiene in TMC-1.

Discovery of CH2CCHC4H and a rigorous detection of CH2CCHC3N in TMC-1 with the QUIJOTE line survey

“…The recent results obtained towards TMC-1 with the Yebes 40m radio telescope through the QUIJOTE 1 line survey (Cernicharo et al 2021a) and those of the Green Bank 100m telescope with the GOTHAM survey (McGuire et al 2018) show that this source presents a paramount challenge to our understanding of the chemical processes in cold prestellar cores. Several cyclic molecules have been detected such as cyclopentadiene and indene (Cernicharo et al 2021b), as well as ortho-benzyne (Cernicharo et al 2021a), the cyano derivatives of cyclopentadiene, benzene, and naphthalene (McGuire et al 2018;McCarthy et al 2021;Lee et al 2021;McGuire et al 2021), and the ethynyl derivatives of cyclopentadiene (Cernicharo et al 2021c). Moreover, several extremely abundant hydrocarbons such as propargyl (Agúndez et al 2021), vinyl acetylene (Cernicharo et al 2021d), and allenyl acetylene (Cernicharo et al 2021e) have also been discovered towards TMC-1.…”

Discovery of HCCCO and C5O in TMC-1 with the QUIJOTE line survey

“…Recent observations of the molecular cloud TMC-1 with the Yebes 40m (Cernicharo et al, 2021a) and Green Bank (McGuire et al , 2018) radio telescopes have shown that this source presents a paramount challenge to our understanding of the chemical processes in cold prestellar cores. The detection of cyclopentadiene and indene (Cernicharo et al, 2021b), orthobenzyne (Cernicharo et al, 2021a), the cyano derivatives of cyclopentadiene, benzene and naphthalene (McGuire et al , 2018;McCarthy et al, 2021;Lee et al, 2021;McGuire et al , 2021), the ethynyl derivatives of cyclopentandiene (Cernicharo et al, 2021c), together with the discovery of extremely abundant hydrocarbons such as propargyl (Agúndez et al , 2021a), vinyl acetylene (Cernicharo et al, 2021d), and allenyl acetylene (Cernicharo et al, 2021e) suggest that key chemical processes involving hydrocarbons (radical, neutral, and/or ionic species) were not considered in previous chemical networks. Most of these species were not predicted to have a significant abundance.…”