Cocondensation of carbon disulfide with high-frequency discharged argon at 4 K produced carbon monosulfide and atomic Sulfur, which reacted spontaneously upon annealing to form the carbon trisulfide molecule as identified from the multiplets observed in mixed C-12, C-13 and S-32, S-34 isotopic spectra. On the basis of isotopic substitution and theoretical frequency calculations, infrared absorptions at 1263.3 and 570.1 cm(-1) were assigned to predominantly C=S stretching and bending vibrations Of CS3 in solid argon. The CS3 molecule, which was calculated to have a singlet ground state with C-2v symmetry, dissociated to form the weakly bound SCS-S complex upon visible light irradiation.