First isolation and spectroscopic observation of thiofulminic acid (HCNS)

A study was conducted to demonstrate the first preparation of the parent nitrile sulfide, thiofulminic acid (HCNS) and its identification by infrared (IR) spectroscopy. These sulfides were identified in cryogenic matrices based on an IR band in the C-N stretching region or on UV bands between 240 and 335 nm. The existence of HCNS and other nitrile sulfides was established indirectly by neutralization-reionization mass spectrometry. UV irradiation of the precursor, 1,2,5-thiadiazole at 254 nm led to the formation of HCNS in cryogenic Ar and Kr matrices. New and strong absorption bands were observed in the IR spectrum after pyrolysis. These bands were assigned to three or four fundamental vibrational modes of HCNS on the basis of high-level ab initio calculations. Theoretical calculations also supported the assumption that the new bands were due to hydrogen-bonded complex formation between HCNS and HCN.