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Description
Observations of TMC-1 with the Yebes 40m radio telescope in the 31.0-50.3GHz range allowed the detection of 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_02_-1_01_ rotational transition of H_2_CCN point to that the lines arise from the deuterated cyanomethyl radical, HDCCN. Using Fourier transform microwave spectroscopy experiments combined with electric discharges we have succeeded in producing the radical HDCCN in the laboratory and observed its 1_01_-0_00_ and 2_02_-1_01_ rotational transitions. From our observations and assuming a rotational temperature of 5K, we derive an abundance ratio H_2_CCN/HDCCN=20. The high abundance of the deuterated form of H_2_CCN is well accounted for by a standard gas-phase model where deuteration is driven by deuteron transfer from the H_2_D+ molecular ion.
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