Discovery of CH<sub>3</sub>CHCO in TMC-1 with the QUIJOTE line survey
R. Fuentetaja, Celina Bermúdez, C. Cabezas, M. Agúndez, B. Tercero, N. Marcelino, J. R. Pardo, L. Margulès, R. A. Motiyenko, Jean‐Claude Guillemin, P. de Vicente, J. Cernicharo
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 3 σ level. We derived a column density for CH 3 CHCO of N = 1.5 × 10 11 cm −2 and a rotational temperature of 9 K. Hence, the abundance ratio between ketene and methyl ketene, CH 2 CO/CH 3 CHCO, is 93. This species is the second C 3 H 4 O isomer detected. The other, trans-propenal (CH 2 CHCHO), corresponds to the most stable isomer and has a column density of N = (2.2 ± 0.3)×10 11 cm −2 , which results in an abundance ratio CH 2 CHCHO/CH 3 CHCO 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.