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Detection of deuterated methylcyanoacetylene, CH 2 DC 3 N, in TMC-1.

Authors :: Cabezas C
Roueff E
Tercero B
Agúndez M
Marcelino N
de Vicente P
Cernicharo J
Source :: Astronomy and astrophysics [Astron Astrophys] 2021 Jun 21; Vol. 650. Date of Electronic Publication: 2021 Jun 21 (Print Publication: 2021).
Publication Year :: 2021
Abstract: We report the first detection in space of the single deuterated isotopologue of methylcyanoacetylene, CH <subscript>2</subscript> DC <subscript>3</subscript> N. A total of fifteen rotational transitions, with J = 8-12 and K <subscript>a</subscript> = 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) × 10 <superscript>10</superscript> cm <superscript>-2</superscript> . The abundance ratio between CH <subscript>3</subscript> C <subscript>3</subscript> N and CH <subscript>2</subscript> DC <subscript>3</subscript> N is ∼22. We also theoretically computed the principal spectroscopic constants of <superscript>13</superscript> C isotopologues of CH <subscript>3</subscript> C <subscript>3</subscript> N and CH <subscript>3</subscript> C <subscript>4</subscript> H and those of the deuterated isotopologues of CH <subscript>3</subscript> C <subscript>4</subscript> H for which we could expect a similar degree of deuteration enhancement. However, we have not detected either CH <subscript>2</subscript> DC <subscript>4</subscript> H nor CH <subscript>3</subscript> C <subscript>4</subscript> D nor any <superscript>13</superscript> 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 <subscript>2</subscript> D <superscript>+</superscript> .