HNCS, the lowest energy isomer, was detected in the Galactic center source Sgr B2(OH) by
M. A. Frerking, R. A. Linke, and P. Thaddeus,
Interstellar Isothiocyanic Acid
Astrophys. J. 234, (1979), L143.
They detected 5 successive K_a = 0 a-type transitions with J = 7 – 6 to 12 – 11. The molecule is only abundant in the colder parts of the source.

The detection in Sgr B2 is described below in the HSCN section.

G. R. Adande, D. T. Halfen, L. M. Ziurys, D. Quan, and E. Herbst
report on
Observations of the [HNCS]/[HSCN] Ratio in Sgr B2 and TMC-1: Evidence for Low-temperature Gas-phase Chemistry
Astrophys. J. 725, (2010), 561.
The 12 m ARO telescope probably probes the envelope of Sgr B2, where they found ratios of 2 to 7, whereas they found a ratio close to 1 in the dark molecular cloud TMC-1.

L. Velilla Prieto, C. Sánchez Contreras, J. Cernicharo, M. Agúndez, G. Quintana-Lacaci, J. Alcolea, V. Bujarrabal, F. Herpin, K. M. Menten, and F. Wyrowski
report on
New N-bearing species towards OH 231.8+4.2 — HNCO, HNCS, HC3N, and NO
Astron. Astrophys. 575, (2015), Art. No. A84.
The molecules were identified in the course of a line survey of the circumstellar envelope of this O-rich AGB star, aka QX Pup, with the IRAM 30 m dish at 3 to 1 mm.

M. Sanz-Novo, V. M. Rivilla, I. Jiménez-Serra, J. Martín-Pintado, L. Colzi, S. Zeng, A. Megías, Á. López-Gallifa, A. Martínez-Henares, S. Massalkhi, B. Tercero, P. de Vicente, D. San Andrés, S. Martín, and M. A. Requena-Torres
announced the
Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺
Astrophys. J. 965, Art. No. 149 (2024).
The results were obtained in the course of a molecular line survey of the Galactic Center molecular cloud G+0.693–0.027 employing the Yebes 40 m and IRAM 30 m radio telecopes. The K_a = 0 lines of HOCS⁺ were blended with those of HNC³⁴S because of nearly identical values of B + C. The transitions cover 34 to 161 GHz with J“ = 2, 3, 6 − 13. The contribution of HNC³⁴S could be accounted for accurately through lines of HNCS, OCS, and OC³⁴S and turned out to be less than that of HOCS⁺. Several lines are slightly or more severely blended in addition, but this is in most cases also well accounted.

Contributor(s): H. S. P. Müller; 09, 2009; 02, 2024; 04, 2024

The detection of HSCN, the second isomer, has been reported by
D. T. Halfen, L. M. Ziurys, S. Brünken, C. A. Gottlieb, M. C. McCarthy, and P. Thaddeus,
Detection of a New Interstellar Molecule: Thiocyanic Acid HSCN
Astrophys. J. 702, (2009), L124.
The Arizona Radio Observatory 12 m telescope has been employed to detect the K_a = 0, J = 6 – 5 to 12 – 11 transitions; the next two transitions were also sought for, but were too weak to be detected, indicating again fairly low rotational temperatures. Observations have been made toward the Galactic center source Sgr B2(N). Though more than 3000 K higher in energy than HNCS, it is only lower in abundance by a factor of three. HNCS was also detected in this source.

J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, R. Fuentetaja, N. Marcelino, and P. de Vicente
announced the
Discovery of thiofulminic acid with the QUIJOTE line survey: A study of the isomers of HNCS and HNCO in TMC-1
Astron. Astrophys. 682, (2024), Art. No. L4.
The authors detect DSCN and H³⁴SCN, which are about a factor of 40 lower in abundance that the main isotopolog.

Contributor(s): H. S. P. Müller; 09, 2009; 02, 2024

J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, R. Fuentetaja, N. Marcelino, and P. de Vicente
announced the
Discovery of thiofulminic acid with the QUIJOTE line survey: A study of the isomers of HNCS and HNCO in TMC-1
Astron. Astrophys. 682, (2024), Art. No. L4.
The molecule was identified in the course of a line survey carried out with the Yebes 40 m and IRAM 30 m dishes. Three transitions, J = 3 − 2 (~36.9 GHz), 4 − 3 (~49.2 GHz), and 6 − 5 (~73.8 GHz) were detected with good to reasnable signal-to-noise ratios. HNCS is anout a factor of 36 more abundant, while for HSCN the factor is about 92.

Contributor(s): H. S. P. Müller; 02, 2024