2025A&A...698L..24C

We present the detection of propenethial (CH₂CHCHS), the sulphur analogue of interstellar acrolein (CH₂CHCHO), towards TMC-1. The detection of this new sulphur molecule in TMC-1 is based on the data derived from rotational spectroscopy laboratory experiments, including new data in the millimetre wave domain, which are also presented in this work. Propenethial was observed in the cold dark cloud TMC-1 using data from the ongoing QUIJOTE line survey, which is being carried out with the Yebes 40m telescope. A total of nine rotational transitions with J = 6 up to 9 and K_a = 0 and 1 were detected in the 31.0-50.4 GHz range. We derive a total column density for propenethial of (4.4 ± 0.4) × 10¹⁰ cm^–2, which is 2, 6.8, and 27 times smaller than those for CH₃CHS, HCCHS, and NCCHS, which are the other thioaldehyde derivatives detected in TMC-1. The abundance ratio found in TMC-1 between the aldehyde counterpart, acrolein, and propenethial is 4.7, which is also different from those found for other pairs of aldehydes-thioaldehydes in this source. Our investigation of possible chemical formation pathways suggests that CH₂CHCHS likely results from a combination of gas- and surface-phase reactions.