NNS is produced by flash vacuum pyrolysis of 5-aryl-1,2,3,4-thiatriazoles 1, 3, 5, and 7 and 5-phenoxy-1,2,3,4-thiatriazole (9). The Ar matrix infrared spectrum shows nu(NN) at 2039 cm-1 and nu(NS) at 752 cm-1. The experimental data are compared with high-level ab initio as well as semiempirical (MNDO) calculated structural and vibrational data. NNS is destroyed photochemically or on heating to 160 K.