A combination of matrix isolation technique and Fourier transform infrared spectroscopy has been used to study the low-temperature photochemistry of isothiocyanic acid HNCS. Near UV photolysis with a medium-pressure mercury lamp of the matrix isolated HNCS/DNCS precursor in nitrogen and argon led to the formation of two unobserved, so far, isomers: thiocyanic acid HSCN and isothiofulminic acid HSNC and their deuterated analogs. Both species are formed as primary products presumably via two reaction channels: formation of the [(HNCS)-N-...] and hydrogen migration leading to the HSCN molecule and formation of the [HNC . . .S] followed by rearrangement to HSCN and HSNC species.