Letter to the Editor

Discovery of propenethial (CH₂CHCHS) in TMC-1

The sulphur analogue of acrolein

¹ Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
² Department of Analytical Chemistry, University of Chemistry and Technology, Technická 5, 166 28 Prague 6, Czech Republic
³ Observatorio Astronómico Nacional (OAN, IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
⁴ Observatorio de Yebes, IGN, Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain

^⋆ Corresponding authors: carlos.cabezas@csic.es; j.cernicharo@csic.es; lucie.kolesnikova@vscht.cz

Received: 20 March 2025
Accepted: 10 May 2025

Abstract

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.