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 only detection in a different source, Sgr B2(N), is described below in the HSCN section.

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.

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