===== On the Detection of Ethynylcyclopentadienes in the ISM =====

J. Cernicharo, M. Agúndez, R. I. Kaiser, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, and P. de Vicente\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/202142226|Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: Abundances of CCH and CN derivatives of hydrocarbon cycles]]**\\
//Astron. Astrophys.// **655**, Art. No. L1 (2021).\\
Both low-lying isomers, 1- and 2-ethynylcyclopentadiene, were indentified in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 31.0 and 50.3 GHz. 11 and 21 //a//-type transitions respectively with 8 ≤ //J// ≤ 14 and //K<sub>a</sub>// ≤ 3 were reported to be unblended or only slightly blended. The lines have modest to reasonable signal-to-noise ratios. A value of //T//<sub>rot</sub> = 9 ± 1 K was derived. The 2-isomer is about 1.4 times more abundant than the 1-isomer and about a factor of 6 less abundant than cyclopentadiene. The authors also rederive columndensities for the isoelectronic cyanocyclopentadienes. They are less abundant than their respective ethynyl relatives by factors of 4.5 and 15 for the 1- and 2-isomers, respectively. Phenylethyne was identified tentatively; it would be at most only a factor of 2 more abundant than phenyl cyanide, aka benzonitrile.\\
\\

----

Contributor(s): H. S. P. Müller; 12, 2021

----