N. Kaifu, H. Suzuki, M. Ohishi, T. Miyaki, S.-I. Ishikawa, T. Kasuga, M. Morimoto, and S. Saito
reported on the
Detection of Intense Unidentified Lines in TMC-1
Astrophys. J. 317, L111–L114 (1987);
obtained in the course of a molecular line survey carried out with the 45 m Nobeyama telescope which ultimately covered the 8 – 50 GHz range.

Laboratory spectroscopic investigations by
S. Saito, K. Kawaguchi, S. Yamamoto, M. Ohishi, H. Suzuki, and N. Kaifu
lead to the
Laboratory Detection and Astronomical Identification of a New Free Radical, CCS ³Σ^–
Astrophys. J. 317, L115–L118 (1987).
Four lines from the line survey mentioned above were assigned to C₂S. These were the N_J = 1₂ – 2₁, 3₃ – 2₂, 4₃ – 3₂, and 3₄ – 2₃ transitions at 22344, 38866, 43981, and 45379 MHz, respectively. Please note: the labeling of the 2₁ level follows that of the CDMS catalog entry. This level is labeled 0₁ in the original work.
The authors also assigned several U-lines from two molecular line surveys of Sagittarius B2 in the 3 and 2 mm regions to C₂S.
Finally, the CC³⁴S isotopolog was also detected toward TMC-1 by its 1₂ – 2₁ transition at 21930 MHz.

In addition, laboratory spectroscopic investigations by
S. Yamamoto, S. Saito, K. Kawaguchi, N. Kaifu, and H. Suzuki
lead to the
Laboratory Detection of a New Carbon-chain Molecule C₃S and its Astronomical Identification
Astrophys. J. 317, L119–L121 (1987).
The J = 4 – 3, 7 – 6, and 8 – 7 transitions were identified at 23123, 40465, and 46246 MHz, respectively.

C₂S, along with C₃S, were also detected with the IRAM 30 m telescope in the circumstellar envelope of the carbon-rich late-type star CW Leo, also known as IRC +10216 in the course of a molecular line survey in the 3 and 2 mm regions by
J. Cernicharo, M. Guélin, H. Hein, and C. Kahane,
Sulfur in IRC +10216
Astron. Astrophys. 181, L9–L12 (1987).

C₂S was also seen toward several translucent clouds, albeit in only the lower energy transition of two by
B. E. Turner, H.-H. Lee, and E. Herbst,
The Physics and Chemistry of Small Translucent Molecular Clouds.\\ IX. Acetylenic Chemistry
Astrophys. J. Suppl. Ser. 115, 91–118 (1998).

The two ¹³C isotopomers were detected with the Nobeyama 45 m telescope toward TMC-1 by
N. Sakai, M. Ikeda, M. Morita, T. Sakai, S. Takano, Y. Osamura, and S. Yamamoto,
Production Pathways of CCS and CCCS Inferred from Their ¹³C Isotopic Species
Astrophys. J. 663, 1174–1179 (2007).
The C¹³CS isotopolog is highly depleted, and it has not been detected in L1521E, whereas ¹³CCS was seen.

C₃S, along with C₂S, were also detected with the IRAM 30 m telescope in the circumstellar envelope of the carbon-rich late-type star CW Leo, also known as IRC +10216 in the course of a molecular line survey in the 3 and 2 mm region by
J. Cernicharo, M. Guélin, H. Hein, and C. Kahane,
Sulfur in IRC +10216
Astron. Astrophys. 181, L9–L12 (1987).

The detection of the ³⁴S isotopolog in the course of the Nobeyama 45 m line survey was mentioned first by
M. Ohishi and N. Kaifu,
Chemical and Physical Evolution of Dark Clouds. Molecular Spectral Line Survey toward TMC-1
Faraday Discuss. 190, 205–216 (1998).

C₃S was deteceted very recently in a warm cloud by
B. Tercero, J. Cernicharo, J. R. Pardo, and J. R. Goicoechea,
A line confusion limited millimeter survey of Orion KL\\ I. Sulfur carbon chains
Astron. Astrophys. 517, Art. No. A96 (2010).

M. Agúndez, J. Cernicharo, and M. Guélin
reported on
New molecules in IRC +10216: confirmation of C₅S and tentative identification of MgCCH, NCCP, and SiH₃CN
Astron. Astrophys. 570, Art. No. A45 (2014).
The J + 1 → J transitions with J = 43, 44, and 45 of C₅S were identified in the course of a 3 mm line survey with the IRAM 30 m telescope near 81.2, 83.0, and 84.9 GHz. The first transition is blended. The almost similar column densities between two carbon chain molecules, here C₅S and C₃S, are very unusual, though not unprecedented.

M. B. Bell, L. W. Avery, and P. A. Feldman
had reported on
C₃S and C₅S in IRC +10216
Astrophys. J. 417, L37–L40 (1993).
A line observed with the NRAO 43 m telecope near 24.0 GHz in the course of a molecular line survey was assigned to the J = 13 – 12 transition of C₅S. The authors state in the abstract: “Assuming the observed feature is due to C₅S, we find that N(C₅S)/N(C₃S) ≈ 0.5.” Confirmation of this finding or identification of further transitions at shorter wavelengths will be useful.

The molecule was recently also identified in TMC-1 by
J. Cernicharo, C. Cabezas, M. Agúndez, B. Tercero, J. R. Pardo, N. Marcelino, J. D. Gallego, F. Tercero, J. A. López-Pérez, and P. de Vicente
TMC-1, the starless core sulfur factory: Discovery of NCS, HCCS, H₂CCS, H₂CCCS, and C₄S and detection of C₅S
Astron. Astrophys. 648, Art. No. L3 (2021).
C₅S was identified through 5 rotational transitions with J“ = 16 to 20 and with modest to good signal-to-noise ratio (one slightly blended, one severely blended) in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 32.8 and 49.2 GHz. See below for statements on the column densities.

J. Cernicharo, C. Cabezas, M. Agúndez, B. Tercero, J. R. Pardo, N. Marcelino, J. D. Gallego, F. Tercero, J. A. López-Pérez, and P. de Vicente
reported on
TMC-1, the starless core sulfur factory: Discovery of NCS, HCCS, H₂CCS, H₂CCCS, and C₄S and detection of C₅S
Astron. Astrophys. 648, Art. No. L3 (2021).
C₄S was identified through for fine structure transitions with N” = 9 to 12 and J = N + 1 and with moderate to good signal-to-noise ratio (one slightly blended, one severely blended) in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 32.8 and 49.2 GHz. The column density of C₄S is slightly lower than that of C₅S, and about factors of 340 and 1350 lower than those of C₃S and C₂S, respectively.

Contributor(s): H. S. P. Müller; 09, 2012; 07, 2018; 09, 2020; 04, 2021