===== On the Detection of Propyne, CH3CCH, in Space =====

Propyne, CH<sub>3</sub>CCH, also known as methylacetylene, was among the molecules detected early by radioastronomical means. An initial account on its detection was presented at an NRAO symposium at the University of Virginia, Nov. 4−7, 1971 by\\
D. Buhl and L. E. Snyder\\
**[[https://cdms.astro.uni-koeln.de/classic/predictions/daten/CH3CCH/Buhl_and_Snyder_1973.pdf|The Detection of a MM-Wave Transition of Methylacetylene]]**\\
in: M.A. Gordon, L.E. Snyder (Eds.), Molecules in the Galactic Environment, 1973, 187−195.\\
The //J// = 5 – 4 transition with //K// = 0 was observed with the 36 foot (11 m) NRAO dish at 85457.3 MHz toward Sagittarius B.\\

J. M. Hollis, L. E. Snyder, D. H. Blake, F. J. Lovas, R. D. Suenram, and B. L. Ulich\\
identified the //J// = 9 – 8 transitions with //K// = 0 to 3 near 153.8 GHz employing the same instrument in their report on\\
**[[https://ui.adsabs.harvard.edu/abs/1981ApJ...251..541H|New Interstellar Molecular Transitions in the 2 Millimeter Range]]**\\
//Astrophys. J.// **251**, 541–548 (1981).\\

E. Churchwell and J. M. Hollis\\
studied\\
**[[https://ui.adsabs.harvard.edu/abs/1983ApJ...272..591C|The Kinetic Temperature and CH<sub>3</sub>CCH Column Density Profiles in Sgr B2, Orion and DR 21]]**\\
//Astrophys. J.// **272**, 591–608 (1983).\\
These three high-mass star-forming regions were studied with the same instrument covering the //J// = 5 – 4 and 6 – 5 transitions.\\

Further sources, including the dark Taurus Molecular Cloud 1 (TMC-1), were studied by\\
T. B. H. Kuiper, E. N. R. Kuiper, D. F. Dickinson, B. E. Turner, and B. Zuckerman\\
**[[https://ui.adsabs.harvard.edu/abs/1984ApJ...276..211K|Methyl Acetylene as a Temperature Probe for Dense Interstellar Clouds]]**\\
//Astrophys. J.// **276**, 221–220 (1984);\\
and by\\
J. Askne, B. Höglund, Å. Hjalmarson, and W. M. Irvine\\
**[[https://ui.adsabs.harvard.edu/abs/1984A&A...130..311A|Methyl Acetylene as a Temperature Probe in Molecular Clouds]]**\\
//Astron. Astrophys.// **130**, 311–318 (1984).\\

B. E. Turner, E. Herbst, and R. Terzieva\\
investigated\\
**[[https://doi.org/10.1086/313301|The Physics and Chemistry of Small Translucent Molecular Clouds. XIII. The Basic Hydrocarbon Chemistry]]**\\
//Astrophys. J. Suppl. Ser.// **126**, 427–460 (2000).\\
Propyne was detected in the sources CB 17 and CB 228; only an upper limit was determined for CB 24.\\

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The molecules was also detected in the circumstellar envelopes of late-type stars. The examples refer to a protoplanetary nebula, the asymptotic giant branch star CW Leonis, and a planetary nebula.\\
J. R. Pardo and J. Cernicharo\\
**[[https://doi.org/10.1086/509568|Molecular Abundances in CRL 618]]**\\
//Astrophys. J.// **654**, 978–987 (2007).\\
M. Agúndez, J. P. Fonfría, J. Cernicharo, J. R. Pardo, and M. Guélin\\
**[[https://doi.org/10.1051/0004-6361:20078956|Detection of Circumstellar CH<sub>2</sub>CHCN, CH<sub>2</sub>CN, CH<sub>3</sub>CCH, and H<sub>2</sub>CS]]**\\
//Astron. Astrophys.// **479**, 493–501 (2008).\\
D. R. Schmidt and L. M. Ziurys\\
**[[https://doi.org/10.3847/2041-8213/ab3663|Exotic Carbon Chemistry in a Planetary Nebula: the Unusual Case of K4-47]]**\\
//Astrophys. J. Lett.// **881**, Art. No. L38 (2019).\\

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The isotopolog CH<sub>3</sub>C<sup>13</sup>CH was found serendipitously by\\
F. Combes, M. Gerin, A. Wootten, G. Wlodarczak, F. Clausset, and P. J. Encrenaz,\\
in their search for\\
**[[https://ui.adsabs.harvard.edu/abs/1987A&A...180L..13C|Acetone in Interstellar Space]]**\\
//Astron. Astrophys.// **180**, L13–L16 (1987).\\

All three isotopomers were found by\\
D. T. Halfen, N. J. Woolf, and L. M. Ziurys\\
in their investigation of\\
**[[https://doi.org/10.3847/1538-4357/aa816b|The <sup>12</sup>C/<sup>13</sup>C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry]]**\\
//Astrophys. J.// **845**, Art. No. L158 (2017).\\
Other reports include, e.g., the letter by Schmidt and Ziurys, see above.

The report by\\
M. Gerin, F. Combes, G. Wlodarczak, P. Encrenaz, and C. Laurent\\
on\\
**[[https://ui.adsabs.harvard.edu/abs/1992A&A...253L..29G|Interstellar detection of deuterated methyl acetylene,]]**\\
//Astron. Astrophys.// **253**, L29–L32 (1992)\\
refers to the methyl deuterated isotopolog, which was detected with the IRAM 30 m dish in TMC-1.\\

A. J. Markwick, S. B. Charnley, H. M. Butner, T. J. Millar\\
detected\\
**[[https://doi.org/10.1086/432415|Interstellar CH<sub>3</sub>CCD]]**\\
//Astrophys. J. Lett.// **627**, L117−L120 (2005).\\
The authors used the OSO 20 m dish for a detection in TMC-1.\\

M. Agúndez, E. Roueff, C. Cabezas, J. Cernicharo, and N. Marcelino\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/202140843|First detection of doubly deuterated methyl acetylene (CHD<sub>2</sub>CCH and CH<sub>2</sub>DCCD)]]**\\
//Astron. Astrophys.// **649**, Art. No. A 171 (2021).\\
The identifications were made in the course of a molecular line survey of L483 at 3 mm carried out with the IRAM 30 m radio telescope. The survey samples cold material; the presence of the embedded Class 0 infrared source IRAS 18148−0440 is not visible in these data. 9 and 8 //a//-type transition frequencies with 4 ≤ //J// ≤ 7 and //K<sub>a</sub>// ≤ 1 were reported. The column density ratios of CH<sub>3</sub>CCH with CH<sub>2</sub>DCCH, CH<sub>3</sub>CCD, CHD<sub>2</sub>CCH, and CH<sub>2</sub>DCCD are about 5, 16, 34, and 42, respectively.\\


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Contributor(s): H. S. P. Müller 03, 2020; 06, 2021

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