Authors: Cabezas, C.; Roueff, E.; Tercero, B.; Agundez, M.; Marcelino, N.; de Vicente, P.; Cernicharo, J.


Publication date: 2021/06/21

DOI: 10.1051/0004-6361/202141371

Abstract: 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)x10(10) cm(-2). The abundance ratio of CH3C3N to CH2DC3N is similar to 22. We also theoretically computed the principal spectroscopic constants of C-13 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 C-13 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+.