The thioformyl cation, HCS+, has been observed
in the ISM prior to the laboratory. It was observed toward
Ori KL and Sgr B2 covering lines up to J = 6 – 5:
P. Thaddeus, M. Guélin, and R. A. Linke,
Three New 'Nonterrestrial' Molecules
Astrophys. J. 480, L71–L74 (1997).