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# Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and its first detection in the ISM

Astronomy & Astrophysics
EDP Sciences

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### Abstract

Context. Small imines containing up to three carbon atoms are present in the interstellar medium (ISM). As alkynyl compounds are abundant in this medium, propargylimine (2-propyn-1-imine, HC ≡C−CH =NH) thus represents a promising candidate for a new interstellar detection.

Aims. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of propargylimine in its ground vibrational state in order to obtain a highly precise set of rest frequencies and to search for it in space.

Methods. The rotational spectra of E and Z geometrical isomers of propargylimine have been recorded in the laboratory in the 83–500 GHz frequency interval. The measurements have been performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic quantities. We searched for propargylimine at 3 mm and 2 mm in the spectral survey of the quiescent giant molecular cloud G+0.693-0.027 located in the central molecular zone, close to the Galactic centre.

Results. About 1000 rotational transitions have been recorded for the E- and Z-propargylimine, in the laboratory. These new data have enabled the determination of a very accurate set of spectroscopic parameters including rotational, quartic, and sextic centrifugal distortion constants. The improved spectral data allowed us to perform a successful search for this new imine in the G+0.693-0.027 molecular cloud. Eighteen lines of Z-propargylimine were detected at level >2.5 σ, resulting in a column-density estimate of N = (0.24 ± 0.02) × 10 14 cm −2. An upper limit was retrieved for the higher energy E isomer, which was not detected in the data. The fractional abundance (with respect to H 2) derived for Z-propargylimine is 1.8 × 10 −10. We discuss the possible formation routes by comparing the derived abundance with those measured in the source for possible chemical precursors.

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### Author and article information

###### Journal
Astronomy & Astrophysics
A&A
EDP Sciences
0004-6361
1432-0746
August 2020
August 20 2020
August 2020
: 640
: A98
###### Article
10.1051/0004-6361/202038083
0e61a477-7f3c-45ac-85e4-2b4ed89a0de5
© 2020
###### Product
Self URI (article page): https://www.aanda.org/10.1051/0004-6361/202038083