Rotational spectroscopy of malononitrile and its corresponding monoisocyanide isomer, isocyanoacetonitrile

R A Motiyenko,E A Alekseev,L Margulès,J.-C Guillemin,I A Armieieva

doi:10.1051/0004-6361/201834587

Abstract

Context. Nitriles constitute almost 20% of the molecules observed in the interstellar medium, whereas only one dinitrile and one isocyanonitrile compound have been detected up to now. The lack of detections of such compounds may be partially explained by the lack of accurate spectroscopic data on their rotational spectra.Aims. Two small seven-atom dinitriles, malononitrile NCCH2CN and isocyanoacetonitrile NCCH2NC, were chosen as target species for this study. For malononitrile the goal of the study is to systematize all the previous measurements, and to extend the measurements to the sub-millimeter wavelength range. The spectrum of isocyanoacetonitrile has not been studied before.Methods. The rotational spectra of the two molecules were measured in the frequency range 150–660 GHz using the Lille fast-scan spectrometer. The spectroscopic study was supported by high-level theoretical calculations on the structure of these molecules and their harmonic force field.Results. Accurate frequency predictions for malononitrile and isocyanoacetonitrile were calculated on the basis of the analysis of their rotational spectra. The influence of the spin statistics on the intensities of the lines of malononitrile was taken into account. The provided line lists and sets of molecular parameters meet the needs of astrophysical searches for the two molecules.

Highlights

One dicarbonitrile, the protonated cyanogen NCCNH+ (Agúndez et al 2015), and one isocyano nitrile, isocyanogen, NCNC (Agúndez et al 2018), have been detected in the interstellar medium (ISM) among about 200 other compounds
Compounds such as the cyanomethyl radical CH2CN, Full Tables A.1–A.3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: //cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A162 1 http://www.astro.uni-koeln.de/cdms/molecules the cyanomethylene radical HC2N, the methylene amidogen H2CN, the cyanomethylidyne radical C2N, the CN radical, and the CN anion are present in this medium
This study follows the recording of the millimeter-wave spectrum of methylene bisisocyanide (Motiyenko et al 2012) which anticipated, along with some others (Haykal et al 2013; Samdal et al 2013, 2014; Margulès et al 2018), the possible presence of other isocyanides in the ISM in addition to the detected methyl and ethynyl isocyanides (Cernicharo et al 1988; Kawaguchi et al 1992) and isocyanogen (Agúndez et al 2018)

Summary

Introduction

The protonated cyanogen NCCNH+ (Agúndez et al 2015), and one isocyano nitrile, isocyanogen, NCNC (Agúndez et al 2018), have been detected in the interstellar medium (ISM) among about 200 other compounds. Several dinitrogen compounds are present in the ISM, such as cyanamide (Turner et al 1975), aminoacetonitrile (Belloche et al 2008), and E-cyanomethanimine (Zaleski et al 2013) Compounds such as the cyanomethyl radical CH2CN, Full Tables A.1–A.3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: //cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A162 1 http://www.astro.uni-koeln.de/cdms/molecules the cyanomethylene radical HC2N, the methylene amidogen H2CN, the cyanomethylidyne radical C2N, the CN radical, and the CN anion are present in this medium. These are potentially highly reactive compounds and probably precursors of many nitriles. In the case of compounds with a C3H2N2 formula, the reaction of the cyanomethyl radical with the cyano radical could produce both target compounds, which could be the products of the reaction of the HC2N radical with hydrogen cyanide or hydrogen isocyanide, or produced by many other routes

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Conclusion