Silicon monosulfide, SiS, is a very abundant molecule in the inner regions of the circumstellar envelop of IRC+10216 (CW Leo) where it is thought to be the progenitor of much of the Si-chemistry. It was reported first by
M. Morris, W. Gilmore, P. Palmer, B. E. Turner, and B. Zuckerman,
Detection of Interstellar SiS and a Study of the IRC +10216 Molecular Envelope
Astrophys. J. 199, L47–L51 (1975).
The 11 m Kitt Peak telescope was used to detect the J = 6 – 5 and 5 – 4 transitions near 108.9 and 90.8 GHz, respectively.

The first paper, mentioned in the previous paragraph, also reports on the tentative detection of SiS toward Sgr B2. In the meantime, there have been several reports on SiS in massive star-forming regions.
D. F. Dickinson and E. N. Rodriguez Kuiper
reported on
Interstellar silicon sulfide
Astrophys. J. 247, 112–115 (1981).
The same transitions as above were detected toward Sgr B2, and the 6 – 5 transition was detected toward Orion A.

L. Podio, C. Codella, B. Lefloch, N. Balucani, C. Ceccarelli, R. Bachiller, M. Benedettini, J. Cernicharo, N. Faginas-Lago, F. Fontani, A. Gusdorf, and M. Rosi
reported on
Silicon-bearing Molecules in the Shock L1157-B1: First Detection of SiS around a Sun-like Protostar
MNRAS Lett. 470, L16–L20 (2017).
Six millimeter and submillimeter transitions of SiS were observed with the IRAM 30 m telescope.

A total of seven rare isotopic species has been detected since. These involve ²⁹SiS and Si³⁴S:
L. E. B. Johansson, C. Andersson, J. Ellder, P. Friberg, Å. Hjalmarson, B. Höglund, W. M. Irvine, H. Olofsson, and G. Rydbeck,
Spectral Scan of Orion A and IRC+10216 from 72 to 91 GHz
Astron. Astrophys. 130, 227–256 (1984);
³⁰SiS:
L. M. Ziurys, D. P. Clemens, R. J. Saykally, M. Colvin, H. F. Schaefer,
A Search for Interstellar Silicon Nitride
Astrophys. J. 281, 219–224 (1984);
Si³³S:
C. Kahane, J. Gomez-Gonzalez, J. Cernicharo, and M. Guélin,
Carbon, Nitrogen, Sulfur and Silicon Isotopic Ratios in the Envelope of IRC +10216
Astron. Astrophys. 190, 167–177 (1988);
²⁹Si³⁴S and ³⁰Si³⁴S:
J. Cernicharo, M. Guélin, and C. Kahane,
A λ 2 mm Molecular Line Survey of the C-Star Envelope IRC +10216
Astron. Astrophys. Suppl. 142, 181–215 (2000);
and Si³⁶S:
R. Mauersberger, U. Ott, C. Henkel, J. Cernicharo, and R. Gallino,
The Abundance of ³⁶S in IRC +10216 and its Production in the Galaxy
Astron. Astrophys. 426, 219–227 (2004).

Maser activity in v = 0 of the main isotopic species has been reported first by
C. Henkel, H. E. Matthews, and M. Morris,
SiS Maser Emission from IRC +10216
Astrophys. J. 267, 184–190 (1983).
J. P. Fonfría Expósito, M. Agúndez, B. Tercero, J. R. Pardo, and J. Cernicharo
reported on
High-//J// //v// = 0 SiS Maser Emission in IRC +10216: A New Case of Infrared Overlaps
Astrophys. J. 646, L127–L130 (2006).
Transitions J = 11 – 10, 14 – 13, and 15 – 14 were found to be masing.

Vibrationally excited SiS has been detected by
B. E. Turner,
Detection of Vibrationally Excited SiS in IRC +10216
Astron. Astrophys. 183, L23–L26 (1987).
L. Velilla Prieto, J. Cernicharo, G. Quintana-Lacaci, M. Agúndez, A. Castro-Carrizo, J. P. Fonfría, N. Marcelino, J. Zúñiga, A. Requena, and A. Bastida
reported on
Si-bearing Molecules Toward IRC+10216: ALMA Unveils the Molecular Envelope of CW Leo
Astrophys. J. 805, Art. No. L13 (2015).
In the case of the main isotopic species of SiS, transitions up to v = 7, possibly higher, were detected. In addition, emission lines of vibrationally excited minor isotopic species were reported.

Rovibrational transitions were observed by
R. J. Boyle, J. J. Keady, D. E. Jennings, K. L. Hirsch, and G. R. Wiedemann,
Observations of 13.5 micron Rotation-Vibration Lines of SiS in IRC +10216
Astrophys. J. 420, 863–868 (1994).

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Contributor(s): H. S. P. Müller, 02, 2007; 06, 2008; 07, 2017; 12, 2017.

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