2025MNRAS.539.3257C

The number of sulphur-bearing species detected to date in the interstellar medium (ISM) is small compared to oxygen- and nitrogen-bearing species. In fact, the chemistry of sulphur-bearing molecules is strongly dependent on the depletion of sulphur. One of the main inputs to understand the chemistry of sulphur in the ISM is to unveil new molecules containing this element as well as to understand their formation paths. For this purpose, we investigate the rotational spectrum of the HCCSO radical, which seems to be a potential candidate for observation in the molecular clouds where the simpler analogue, HSO, has already been detected. The HCCSO radical has been produced by an electric discharge of thionyl chloride (Cl$_2$SO) and acetylene (HCCH) in argon, and its rotational spectrum between 11 and 40 GHz has been characterized using a Balle-Flygare narrow band-type Fourier-transform microwave spectrometer. Accurate spectroscopic parameters were derived from the spectral analysis that were employed to obtain reliable frequency predictions for astronomical searches in different sources. We searched for HCCSO in several molecular clouds where HSO has been observed, B1-b, L183, L483, and TMC-1, but did not detect it. The upper limits to its abundance in these sources were derived.