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

L. Bizzocchi (1) , D. Prudenzano (1) , V. M. Rivilla (2) , A. Pietropolli-Charmet (3) , B. M. Giuliano (1) , P. Caselli (1) , J. Martín-Pintado (4) , I. Jiménez-Serra (4) , S. Martin (5, 6) , M. A. Requena-Torres (7, 8) , F. Rico-Villas (4) , S. Zeng (9) , J.-C. Guillemin (10)

1 MPE - Max-Planck-Institut für Extraterrestrische Physik
2 INAF - Istituto Nazionale di Astrofisica
3 University of Ca’ Foscari [Venice, Italy]
4 CSIC - Consejo Superior de Investigaciones Cientificas [España] = Spanish National Research Council [Spain]
5 ESO - European Southern Observatory
6 JAO - Joint ALMA Observatory
7 JHU - Johns Hopkins University
8 Towson University [Towson, MD, United States]
9 RIKEN - RIKEN - Institute of Physical and Chemical Research [Japon]
10 ISCR - Institut des Sciences Chimiques de Rennes

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 sigma, resulting in a column-density estimate of N = (0.24 x 0.02) x 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 x 10(-10). We discuss the possible formation routes by comparing the derived abundance with those measured in the source for possible chemical precursors.

Mots clés: molecular data; methods: laboratory: molecular; methods: observational; techniques: spectroscopic; ISM: clouds; ISM: molecules

Domaines: Chimie

L. Bizzocchi, D. Prudenzano, V. M. Rivilla, A. Pietropolli-Charmet, B. M. Giuliano, et al.. Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and its first detection in the ISM. Astronomy and Astrophysics - A&A, 2020, 640, ⟨10.1051/0004-6361/202038083⟩. ⟨hal-02957734⟩