Detection of deuterated methylcyanoacetylene, CH₂DC₃N, 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 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 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 10 cm −2 . The abundance ratio of CH 3 C 3 N to CH 2 DC 3 N is ∼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 or CH 3 C 4 D, nor any 13 C 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 H 2 D + .

Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey

“…QUIJOTE has now reached a level of sensitivity (0.1-0.3 mK per 38.15 kHz channel across the Q band) that permits the detection of new isotopologues and derivatives of abundant species. Examples of detection and complete spectral characterisation of rare isotopologues through QUIJOTE data are HDCCN (Cabezas et al 2021a), CH 2 DC 3 N (Cabezas et al 2021b), and CH 2 DC 4 H (Cabezas et al 2022a). Although QUIJOTE has not yet reached the confusion limit, special care should be taken when assigning lines to a given molecule as blending with other features often occurs.…”

The QUIJOTE line survey of TMC-1

“…Blank channels correspond to negative features produced in the folding of the frequency switching data (from [25]). QUIJOTE data are: HDCCN [19], CH 2 DC 3 N [20], CH 2 DC 4 H [21]. Although QUIJOTE has not yet reached the confusion limit, special care has to be taken when assigning lines to a given molecule as blending with other features often occurs.…”

Low Energy Isomers and Infrared Spectra Simulations of C4H3N, C4H4N, and C4H5N and Related Ions

“…Some nitrogenated six-membered rings and fused species were reported in the Taurus Molecular Cloud (TMC-1), namely, benzonitrile (C 6 H 5 CN), − two cyanonaphthalene (C 10 H 7 CN) isomers, and 2-cyanoindene (C 9 H 7 CN) . The TMC-1 is a well-studied prestellar molecular cloud in which several molecules have been detected for the first time in the ISM. , The CN group attached to aromatic rings generates a permanent dipole moment which differentiates their rotational spectrum, thus allowing successfully detection of nitrile compounds. Following the observation of the six-membered rings, the highly polar 1-cyanocyclopentadiene (c-C 5 H 5 CN), which contains a five-membered cycle, and 3-cyanopropargyl radical (CH 2 CCCN) were also detected in the same source. − …”