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Description
Small imines containing up to three carbon atoms are present in the interstellar medium. 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. 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 83-500GHz 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 have searched for propargylimine at 3 and 2mm 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. 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 allow us to perform a successful search for this new imine in the G+0.693-0.027 molecular cloud. Eighteen lines of Z-propargylimine have been detected at level >2.5*sigma, resulting in a column density estimate of N=(0.24+/-0.02)x10^-14^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. H_2_) derived for Z-propargylimine is 1.8x10^-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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