SIMBAD references

We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CH₂DC₃N. A total of 15 rotational transitions, with J = 8-12 and K_a = 0 and 1, were identified for this species in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40 m 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)x10¹⁰cm^–2. The abundance ratio of CH₃C₃N to 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 or CH₃C₄D, nor any ¹³C isotopologues. The different observed deuterium ratios in TMC-1 are reasonably accounted for by a gas-phase chemical model where the low temperature conditions favour deuteron transfer through reactions with H₂D⁺.