To elucidate the multifaceted but poorly understood chemistry of the pivotal polysulfur−nitrogen heterocycle, tetrasulfur tetranitride (S₄N₄, 1), its photochemistry was studied in Ar matrices. Thereby two primary intermediates and a secondary one (2−4) were detected, and their UV−vis and IR spectra were identified through specific interconversions of 1−4 that can be induced by selective irradiations. The structures associated with these spectra were assigned with the help of DFT calculations. From these assignments it follows that, under the conditions of the present experiments, the cage structure of 1 transforms into isomeric structures 2−4, one of which is a boat-shaped 8-membered cycle (2), and the two other are novel 6-membered S₃N₃ cycles carrying exocyclic (N)SN (3) or (S)N=S (4) groups, respectively, which have not been previously described. These three intermediates probably play a pivotal role in the formation of the diverse products that are observed in the reactions of S₄N₄ even under mild reaction conditions
