Space and laboratory observation of the deuterated cyanomethyl radical HDCCN

Abstract

Our observations of TMC-1 with the Yebes 40 m radio telescope in the 31.0-50.3 GHz range allowed us to detect a group of unidentified lines, showing a complex line pattern indicative of an open-shell species. {}The observed frequencies of these lines and the similarity of the spectral pattern with that of the 2${}_{0,2}$-1${}_{0,1}$ rotational transition of H${}_2$CCN indicate that the lines arise from the deuterated cyanomethyl radical, HDCCN. Using Fourier transform microwave spectroscopy experiments combined with electric discharges, we succeeded in producing the radical HDCCN in the laboratory and observed its 1${}_{0,1}$-0${}_{0,0}$ and 2${}_{0,2}$-1${}_{0,1}$ rotational transitions. From our observations and assuming a rotational temperature of 5 K, we derive an abundance ratio H${}_2$CCN/HDCCN=20$\pm$4. The high abundance of the deuterated form of H${}_2$CCN is well accounted for by a standard gas-phase model, in which deuteration is driven by deuteron transfer from the H${}_2$D${}^{+}$ molecular ion.

This article was submitted to A&A Letters on 23/12/2020 and accepted for publication on 10/01/2021

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• Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey
• Discovery of the propargyl radical (CH2CCH) in TMC-1: one of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds
• Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1
• The sulphur saga in TMC-1: Discovery of HCSCN and HCSCCH
• Detection of the propargyl radical at lambda 3 mm
• Interstellar detection of the simplest aminocarbyne, H2NC: an ignored but abundant molecule
• Discovery of interstellar 3-cyano propargyl radical, CH2CCCN
• Discovery of CH3CHCO in TMC-1 with the QUIJOTE line survey
• Detection of deuterated methylcyanoacetylene, CH${}_2$DC${}_3$N, in TMC-1
• New deuterated species in TMC-1: Detection of CH2DC4H with the QUIJOTE line survey
• Laboratory observation and astronomical search of 1-cyano propargyl radical, HCCCHCN
• CN and CCH derivatives of ethylene and ethane: Confirmation of the detection of CH${}_3$CH${}_2$CCH in TMC-1