Laboratory Measurements and Astronomical Search for Thioacetamide

Radioastronomical observations allowed for the detection of two amides (formamide and acetamide) and some sulfur-containing molecules (among them, ethanethiol and thioformaldehyde) in the interstellar medium (ISM). To understand how the chemical complexity builds up in the ISM, thioacetamide is a next-step candidate. Therefore, laboratory measurements are necessary to attempt its identification in the millimeter wavelength spectral range. The rotational spectrum of thioacetamide was recorded in the 59.6-110.0 GHz frequency region (5.03-2.72 mm) using a Stark-modulated free-jet absorption spectrometer. The spectrum is complicated by the interaction of the methyl internal rotation with the overall molecular rotation, which splits the lines into two components. Nevertheless, 300 transition lines of the parent species and 42 transition lines of the S-34 isotopologue were assigned, to yield the rotational constants, the quartic centrifugal distortion constants, the N-14 nuclear quarupole coupling constants, and the internal rotation parameters. We searched for thioacetamide emission toward regions associated with the star-forming process, leading to a Sun-like star. More specifically, we used the IRAM 30 m ASAI observations toward the prestellar core L1544 and the outflow shock L1157-B1. The present paper allows us to put constrains on thioacetamide abundances in low-mass star-forming regions, paving the way to future deep astronomical searches.