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

TL;DR

This paper reports the detection of methyl ketene in TMC-1, providing new insights into its abundance, chemical relations with isomers, and potential formation pathways in the interstellar medium.

Contribution

The study is the first to detect methyl ketene in TMC-1 and analyzes its abundance and formation mechanisms through observations and chemical modeling.

Findings

Methyl ketene detected with 19 rotational transitions.

Column density of N=1.5x10^11 cm^-2 and temperature of 9 K.

Abundance ratio CH2CO/CH3CHCO is 93.

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 Ka =< 2 were identified in the frequency range 32.0-50.4 GHz, 11 of which arise above the 3{\sigma} level. We derived a column density for CH3CHCO of N=1.5x10^11 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)x10^11 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.