Detection of deuterated methylcyanoacetylene, CH${}_2$DC${}_3$N, in TMC-1

Abstract

We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CH${}_2$DC${}_3$N. A total of fifteen 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 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 $(8.0\pm 0.4)\times 10^{10}$ cm${}^{-2}$. The abundance ratio between CH${}_3$C${}_3$N and CH${}_2$DC${}_3$N is $\sim$22. We also theoretically computed the principal spectroscopic constants of ${}^{13}$C isotopologues of CH${}_3$C${}_3$N and CH${}_3$C${}_4$H and those of the deuterated isotopologues of CH${}_3$C${}_4$H for which we could expect a similar degree of deuteration enhancement. However, we have not detected either CH${}_2$DC${}_4$H nor CH${}_3$C${}_4$D nor any ${}^{13}$C 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 H${}_2$D${}^{+}$.

Accepted for publication in A&A Letters

References in corpus (14)

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Cited by in corpus (10)

• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey
• Discovery of thiofulminic acid with the QUIJOTE line survey: A study of the isomers of HNCS and HNCO in TMC-1
• Discovery of a new molecular ion, HC7NH+, in TMC-1
• Discovery of interstellar 3-cyano propargyl radical, CH2CCCN
• Doubly substituted isotopologues of HCCCN in TMC-1: Detection of D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN, HCC13C15N, and HC13CC15N
• Study of the HCCNC and HNCCC isotopologs in TMC-1
• New deuterated species in TMC-1: Detection of CH2DC4H with the QUIJOTE line survey
• Chemical variations across the TMC-1 boundary: molecular tracers from translucent phase to dense phase
• Laboratory observation and astronomical search of 1-cyano propargyl radical, HCCCHCN