Volume 586, February 2016
|Number of page(s)||9|
|Section||Interstellar and circumstellar matter|
|Published online||02 February 2016|
A study of the C3H2 isomers and isotopologues: first interstellar detection of HDCCC⋆
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstr. 1, 85748
2 California Institute of Technology, 770 S. Wilson Ave., M/C 100-22, Pasadena, CA 91125, USA
3 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
4 Harvard-Smithsonian Center for Astrophysics, and School of Engineering & Applied Sciences, Harvard University, Cambridge, MA 02138, USA
5 Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received: 28 September 2015
Accepted: 12 November 2015
The partially deuterated linear isomer HDCCC of the ubiquitous cyclic carbene (c-C3H2) was observed in the starless cores TMC-1C and L1544 at 96.9 GHz, and a confirming line was observed in TMC-1 at 19.38 GHz. To aid the identification in these narrow line sources, four centimetre-wave rotational transitions (two in the previously reported Ka = 0 ladder and two new ones in the Ka = 1 ladder) and 23 transitions in the millimetre band between 96 and 272 GHz were measured in high-resolution laboratory spectra. Ten spectroscopic constants in a standard asymmetric top Hamiltonian allow the main transitions of astronomical interest in the Ka ≤ 3 rotational ladders to be calculated to within 0.1 km s-1 in radial velocity up to 400 GHz. Conclusive identification of the two astronomical lines of HDCCC was provided by the VLSR, which is the same as for the normal isotopic species (H2CCC) in the three narrow line sources. In these sources, deuterium fractionation in singly substituted H2CCC (HDCCC/H2CCC ~4−19%) is comparable to that in c-C3H2 (c-C3H2/c-C3HD ~5−17%) and similarly in doubly deuterated c-C3H2 (c-C3D2/c-C3HD ~3−17%), implying that the efficiency of the deuteration processes in the H2CCC and c-C3H2 isomers are comparable in dark clouds.
Key words: astrochemistry / line: identification / ISM: molecules / ISM: clouds
© ESO, 2016
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