Propargylimine In The Laboratory And In Space: Millimetre-wave Spectroscopy And First Detection In The ISM

Molecular structure and principal inertial axes of the Z and E isomers of PGIM. The orange arrow indicates the direction of the electric dipole moment µ and points towards the displacement of the notional negative charge. The modulus is µ = 2.15 D for Z-PGIM and µ = 1.95 D for E-PGIM.

Small imines containing up to three carbon atoms are present in the interstellar medium. As alkynyl compounds are abundant in this medium, propargylimine thus represents a promising candidate for a new interstellar detection.

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 it in space. The rotational spectra of E and Z geometrical isomers of propargylimine have been recorded in 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. The improved spectral data allow us to perform a successful search for this new imine in the quiescent G+0.693-0.027 molecular cloud. Eighteen lines of Z-propargylimine have been 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 (w.r.t. 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.

Luca Bizzocchi, Domenico Prudenzano, Victor M. Rivilla, Andrea Pietropolli-Charmet, Barbara M. Giuliano, Paola Caselli, Jesus Martín-Pintado, Izaskun Jiménez-Serra, Sergio Martín, Miguel A. Requena-Torres, Fernando Rico-Villas, Shaoshan Zeng, Jean-Claude Guillemin
Comments: 15 pages, 6 figures. Accepted for publication in Astronomy & Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2006.08401 [astro-ph.GA] (or arXiv:2006.08401v1 [astro-ph.GA] for this version)
Submission history
From: Luca Bizzocchi [view email]
[v1] Mon, 15 Jun 2020 13:44:59 UTC (402 KB)
https://arxiv.org/abs/2006.08401
Astrobiology, Astrochemistry

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