Letter to the Editor

Discovery of CH₃CHCO in TMC-1 with the QUIJOTE line survey^⋆

¹ Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
e-mail: r.fuentetaja@csic.es; jose.cernicharo@csic.es
² Dept. de Química Física y Química Inorgánica, Facultad de Ciencias – I.U. CINQUIMA, Universidad de Valladolid, Paseo de Belén 7, 47011 Valladolid, Spain
³ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
⁴ Observatorio Astronómico Nacional (OAN, IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
⁵ Université de Lille, Faculté des Sciences et Technologies, Département Physique, Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, 59655 Villeneuve d’Ascq Cedex, France
⁶ Univ. Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR – UMR6226, 35000 Rennes, France

Received: 20 December 2022
Accepted: 2 February 2023

Abstract

We report the detection of methyl ketene towards TMC-1 with the QUIJOTE line survey. Nineteen rotational transitions with rotational quantum numbers ranging from J = 3 up to J = 5 and K_a ≤ 2 were identified in the frequency range 32.0–50.4 GHz, 11 of which arise above the 3σ level. We derived a column density for CH₃CHCO of N = 1.5 × 10¹¹ cm⁻² and a rotational temperature of 9 K. Hence, the abundance ratio between ketene and methyl ketene, CH₂CO/CH₃CHCO, is 93. This species is the second C₃H₄O isomer detected. The other, trans-propenal (CH₂CHCHO), corresponds to the most stable isomer and has a column density of N = (2.2 ± 0.3)×10¹¹ cm⁻², which results in an abundance ratio CH₂CHCHO/CH₃CHCO of 1.5. The next non-detected isomer with the lowest energy is cis-propenal, which is therefore a good candidate for future discovery. We have carried out an in-depth study of the possible gas-phase chemical reactions involving methyl ketene to explain the abundance detected, achieving good agreement between chemical models and observations.