Space and laboratory observation of the deuterated cyanomethyl radical HDCCN

TL;DR

This study reports the detection and laboratory confirmation of the deuterated cyanomethyl radical HDCCN in space, providing insights into its abundance and formation mechanisms in interstellar environments.

Contribution

The paper presents the first astronomical detection and laboratory spectroscopy of HDCCN, along with analysis of its abundance ratio in TMC-1, advancing understanding of interstellar deuteration processes.

Findings

HDCCN detected in TMC-1 with a ratio H2CCN/HDCCN=20±4.

Laboratory spectroscopy confirmed the rotational transitions of HDCCN.

Deuteration explained by standard gas-phase models involving H2D+.

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.