Isothiocyanic acid (HNCS) was observed in Sgr B2 by
Frerking, Linke, and Thaddeus in 1979 via three
lines of its rotational spectrum observed with the
Crawford Hill 7 m telescope
(the site is perhaps best known for its role in the
1965 discovery of the
cosmic microwave background radiation).
HNCS is a periodic analog of isocyanic acid,
HNCO. The other two singly-substituted cases are
HPCO, neither of which has been identified to date.
The thiocyanate ion, SCN-, may form in ices
the same way that cyanate ion, OCN-,
can form, by a proton transfer to a base such as ammonia.