We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CH2DC3N. A total of fifteen rotational transitions, with J = 8-12 and Ka = 0 and 1, were identified for this species in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40m radio telescope. The observed frequencies were used to derive for the first time the spectroscopic parameters of this deuterated isotopologue. We derive a column density of (8.0±0.4)×1010 cm−2. The abundance ratio between CH3C3N and CH2DC3N is ∼22. We also theoretically computed the principal spectroscopic constants of 13C isotopologues of CH3C3N and CH3C4H and those of the deuterated isotopologues of CH3C4H for which we could expect a similar degree of deuteration enhancement. However, we have not detected either CH2DC4H nor CH3C4D nor any 13C isotopologue. The different observed deuterium ratios in TMC-1 are reasonably accounted for by a gas phase chemical model where the low temperature conditions favor deuteron transfer through reactions with H2D+.
@article{arxiv.2106.03404,
title = {Detection of deuterated methylcyanoacetylene, CH$_2$DC$_3$N, in TMC-1},
author = {C. Cabezas and E. Roueff and B. Tercero and M. Agúndez and N. Marcelino and P. de Vicente and J. Cernicharo},
journal= {arXiv preprint arXiv:2106.03404},
year = {2021}
}