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Title: Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and its first detection in the ISM
Authors: Bizzocchi, L.
Prudenzano, D.
Rivilla, V. M.
Pietropolli Charmet, A.
Giuliano, B. M.
Caselli, P.
Martín Pintado, J.
Jiménez Serra, I.
Martín, S.
Requena Torres, M. A.
Rico Villas, F.
Guillemin, J. C.
Keywords: Molecular data;Methods: laboratory: molecular;Methods: observational;Techniques: spectroscopic;ISM: clouds;ISM: molecules
Issue Date: 20-Aug-2020
Publisher: EDP Sciences
DOI: 10.1051/0004-6361/202038083
Published version:
Citation: Astronomy and Astrophysics 640: A98(2020)
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 >2.5σ, resulting in a column-density estimate of N = (0.24 ± 0.02) × 1014 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 H2) 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.
Description: Table of the measured laboratory frequencies is only available at the CDS via anonymous ftp to ( or via
E-ISSN: 1432-0746
ISSN: 0004-6361
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