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 20, 2–10, 1 rotational transition of H2CCN 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 10, 1–00, 0 and 20, 2–10, 1 rotational transitions. From our observations and assuming a rotational temperature of 5 K, we derive an abundance ratio H2CCN/HDCCN = 20 ± 4. The high abundance of the deuterated form of H2CCN is well accounted for by a standard gas-phase model, in which deuteration is driven by deuteron transfer from the H2D+ molecular ion.