Isocyanogen formation in the cold interstellar medium

Abstract

Cyanogen (NCCN) is the simplest member of the dicyanopolyynes group, and has been proposed as a major source of the CN radical observed in cometary atmospheres. Although not detected through its rotational spectrum in the cold interstellar medium, this very stable species is supposed to be very abundant. The chemistry of cyanogen in the cold interstellar medium can be investigated through its metastable isomer, CNCN (isocyanogen). Its formation may provide a clue on the widely abundant CN radical observed in cometary atmospheres. We performed an unbiased spectral survey of the L1544 proto-typical prestellar core, using the IRAM-30m and have analysed, for this paper, the nitrogen chemistry that leads to the formation of isocyanogen. We report on the first detection of CNCN, NCCNH+, C3N, CH3CN, C2H3CN, and H2CN in L1544. We built a detailed chemical network for NCCN/CNCN/HC2N2+ involving all the nitrogen bearing species detected (CN, HCN, HNC, C3N, CNCN, CH3CN, CH2CN, HCCNC, HC3N, HNC3, H2CN, C2H3CN, HCNH+, HC3NH+) and the upper limits on C4N, C2N. The main cyanogen production pathways considered in the network are the CN + HNC and N + C3N reactions. The comparison between the observations of the nitrogen bearing species and the predictions from the chemical modelling shows a very good agreement, taking into account the new chemical network. The expected cyanogen abundance is greater than the isocyanogen abundance by a factor of 100. Although cyanogen cannot be detected through its rotational spectrum, the chemical modelling predicts that it should be abundant in the gas phase and hence might be traced through the detection of isocyanogen. It is however expected to have a very low abundance on the grain surfaces compared to HCN.

accepted in A&A (March 2019)

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Cited by in corpus (15)

• Detection of Interstellar HC${}_4$NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
• Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine
• The complex organic molecular content in the L1498 starless core
• Cyanogen, cyanoacetylene, and acetonitrile in comet 67P and their relationship to the cyano radical
• Interstellar detection of the simplest aminocarbyne, H2NC: an ignored but abundant molecule
• Discovery of interstellar NC4NH+: dicyanopolyynes are indeed abundant in space
• Seeds of Life in Space (SOLIS).VII. Discovery of a cold dense methanol blob toward the L1521F VeLLO system
• The chemistry of H2NC in the interstellar medium and the role of the C + NH3 reaction
• Chemical exploration of Galactic cold cores
• Identification of hot gas around low-mass protostars
• A computational analysis of the reaction of atomic oxygen O(3P) with acrylonitrile
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• The emergence of molecular complexity in star forming regions as seen with ASAI
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO