Rotational spectroscopic study of S-methyl thioformate

Abstract

Context. S-methyl thioformate CH3SC(O)H is a monosulfur derivative of methyl formate, a relatively abundant component of the interstellar medium (ISM). S-methyl thioformate being, thermodynamically, the most stable isomer, it can be reasonably proposed for detection in the ISM. Aims. This work aims to experimentally study and theoretically analyze the ground and first torsional excited states for CH3SC(O)H in a large spectral range for astrophysical use. Methods. S-methyl thioformate was synthesized as a result of a reaction of methyl mercaptan with acetic-formic anhydride. The millimeter-wave spectrum was then recorded for the first time from 150 to 660 GHz with the solid-state spectrometer located at Lille. Results. A set of 3545 lines is determined and combined with 54 previously measured lines in the microwave region, belonging to ground state νt = 0 as well as 1391 transitions in the first excited state of torsion ν18 = 1. Some 164 lines were also assigned to ν18 = 2 for the A-species. A global fit was performed using the BELGI-Cs code taking into account the large splitting of A and E lines due to methyl internal rotation motion with a relatively low barrier, V3 = 127.4846(15) cm−1. Conclusions. Using our spectroscopy work, a deep search of S-methyl thioformate was carried out in the IRAM 30 m and ALMA data of different high-mass star-forming regions (Orion KL and Sgr B2). We derived an upper limit to the CH3SC(O)H column density in these regions.

Determination of the semiexperimental equilibrium structure of 2-acetylthiophene in the presence of methyl internal rotation and substituent effects compared to thiophene

“…It is known in the literature that the barriers to methyl internal rotation in oxygen analogues are higher than those in sulphur analogues. Some examples of the barriers in general cases are dimethyl sulphide (735.8 cm −1 ) 11 vs. dimethyl ether (944.3 cm −1 ) 12 or methyl thioformate (127.5 cm −1 ) 13 vs. methyl formate (370.9 cm −1 ). 14 For molecules containing a furan or thiophene moiety, available examples are 194.1 cm −1 for 2-methylthiophene 15 vs. 416.2 cm −1 for 2-methylfuran, 16 258.8 cm −1 for 3-methylthiophene 17 vs. 380.5 cm −1 for 3-methylfuran, 18 or 248.0 cm −1 for 2,5-dimethylthiophene 19 vs. 439.1 cm −1 for 2,5-dimethylfuran.…”

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS+

“…In recent years, searches for diverse S-bearing molecules of increasing complexity, such as thioformamide (NH 2 CHS; Motiyenko et al 2020), thioacetamide (CH 3 C(S)NH 2 ; Remijan et al 2022), thioacetaldehyde (CH 3 CHS; Margulès et al 2020), and methyl thioformate (CH 3 SC(O)H, Jabri et al 2020), have remained so far unfruitful. All the above aspects align with the fact that almost the entire census of detected interstellar S-bearing molecules are S-analogs of the most abundant O-bearing species.…”

Thiols in the ISM: first detection of HC(O)SH and confirmation of C$_2$H$_5$SH

“…The other one is ethyl mercaptan (hereafter C 2 H 5 SH) which was tentatively detected toward Orion KL (Kolesniková et al 2014). Other searches for complex S-bearing molecules were unsuccessful, such as CH 3 CHS (thioacetaldehyde; Margulès et al 2020), NH 2 CHS (thioformamide; Motiyenko et al 2020) and CH 3 SC(O)H (S-methyl thioformate; Jabri et al 2020).…”