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
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 Ka ≤ 3 were reported to be unblended or only slightly blended. The lines have modest to reasonable signal-to-noise ratios. A value of Trot = 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