Methyl mercaptan, or methanethiol, CH₃SH, was detected in emission with the 7 m Bell Lab telescope toward Sagittarius B2(OH):
R. A. Linke, M. A. Frerking, and P. Thaddeus,
Interstellar methyl mercaptan
Astrophys. J. 232, L139–L142 (1979).
6 features belonging to several more J = 3 –2 and 4 –3 were observed near 75.9 and near 101 GHz. The derived rotational temperature in that source was about 9 K.

Much higher rotational temperatures (about 70 K) were derived in a 3, 2, and 1 mm line survey carried out with SEST:
E. Gibb, A. Nummelin, W. M. Irvine, D. C. B. Whittet, and P. Bergman,
Chemistry of the Organic-Rich Hot Core G327.3–0.6
Astrophys. J. 545, 309–326 (2000).

L. Majumdar, P. Gratier, T. Vidal, V. Wakelam, J.-C. Loison, K. M. Hickson, and E. Caux,
reported on the
Detection of CH₃SH in protostar IRAS 16293-2422
Mon. Not. R. Astron. Soc. 458, 1859–1865 (2016).
The IRAM 30 m telescope was used to study this solar-type pair of proto-stars at 3 mm. Here, an excitation temperature of 32 ± 4 K was derived.

L. F. Rodríguez-Almeida, I. Jiménez-Serra, V. M. Rivilla, J. Martín-Pintado, S. Zeng, B. Tercero, P. de Vicente, Laura Colzi, F. Rico-Villas, S. Martín, and M. A. Requena-Torres
reported on
Thiols in the Interstellar Medium: First Detection of HC(O)SH and Confirmation of C₂H₅SH
Astrophys. J. Lett. 912 (2021), Art. No. L11.
This is the first unumbiguous detection of ethanethiol in the ISM. Ten lines with 2 ≤ J ≤ 6 and K_a ≤ 1 were reported and shown, of which nine were unblended or marginally blended and one line was more blended. The observations were part of an unbiased molecular line survey of the quiescent giant molecular cloud G+0.693−0.027, about 1' north-east of Sagittarius B2(N), carried out with the Yebes 40 m dish at 7 mm and with the IRAM 30 m dish at 3 mm. All lines were modeled quite well employing an LTE fit with T_rot = 14.9 ± 0.5 K. The signal-to-noise ratios of the lines were quite good to very good. The column density of methanol is a factor of ∼24 higher.

H. S. P. Müller, A. Belloche, L.-H. Xu, R. M. Lees, R. T. Garrod, A. Walters, J. van Wijngaarden, F. Lewen, S. Schlemmer, and K. M. Menten,
reported on
Exploring molecular complexity with ALMA (EMoCA): Alkanethiols and alkanols in Sagittarius B2(N2)
Astron. Astrophys. 587, Art. No. A92 (2016).
A line survey of Sgr B2(N) was carried out with ALMA at 3 mm. CH₃SH was not only detected in its ground vibrational state, but also in its first torsionally excited state, even though the CH₃OH/CH₃SH ratio was only about 120. These authors derived a rotational temperature of 180 K in this source.

H. A. Bunn, S. Spezzano, L. H. Coudert, J.-C. Guillemin, Y. Lin, C. P. Endres, B. Billinghurst, O. Pirali, J. Jørgensen, V. Lattanzi, and P. Caselli
reported on
Laboratory Rotational Spectroscopy Leads to the First Interstellar Detection of Singly Deuterated Methyl Mercaptan (CH2DSH)
Astrophys. J. Lett. 980, Art. No. L13 (2025).
The isotopolog was identified in the Protostellar Interferometric Line Survey (PILS) toward the solar-like protostar IRAS 16293−2422 B. Eight lines were detected that were deemed to be unblended or only slightly blended. Several other transitions were covered, but most of them were severely blended. The derived CH₂DSH to CH₃SH ratio is about 0.055. An earlier search for CH₃SD by O. Zhakharenko et al., Astron. Astrophys. 621, Art. No. A114 (2019) was unsuccessful and, with respect to the present finding, not particularly constraining.

Contributor(s): H. S. P. Müller; 10, 2010; 07, 2016; 05, 2021; 02, 2025