The infrared spectra of H 2S 2 and its 266 nm photolysis products are studied in an Ar matrix at 7.5 K. The antisymmetric and symmetric HS-stretching, and the antisymmetric bending of H 2S 2 are assigned at 2556.6, 2553.8 and 880.3 cm −1, respectively. The absorptions appearing during the photolysis at 2463, 2460 and 903 cm −1 are tentatively assigned to the HS 2 radical. The two main dissociation channels are: H 2S 2+ hν → HS 2+H and H 2S 2+ hν → S 2+H 2, with a branching ratio close to 1.