Propyne, CH3CCH, 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
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
New Interstellar Molecular Transitions in the 2 Millimeter Range
Astrophys. J. 251, 541–548 (1981).

E. Churchwell and J. M. Hollis
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
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
Methyl Acetylene as a Temperature Probe in Molecular Clouds
Astron. Astrophys. 130, 311–318 (1984).

B. E. Turner, E. Herbst, and R. Terzieva
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.

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
Molecular Abundances in CRL 618
Astrophys. J. 654, 978–987 (2007).
M. Agúndez, J. P. Fonfría, J. Cernicharo, J. R. Pardo, and M. Guélin
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
Exotic Carbon Chemistry in a Planetary Nebula: the Unusual Case of K4-47
Astrophys. J. Lett. 881, Art. No. L38 (2019).

The isotopolog CH3C13CH was found serendipitously by
F. Combes, M. Gerin, A. Wootten, G. Wlodarczak, F. Clausset, and P. J. Encrenaz,
in their search for
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
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
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
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
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 Ka ≤ 1 were reported. The column density ratios of CH3CCH with CH2DCCH, CH3CCD, CHD2CCH, and CH2DCCD are about 5, 16, 34, and 42, respectively.

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

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