The CH3SO radical was formed from reaction of dimethyl disulfide (CH-3)SSCH3 with microwave-discharged O2) in a flow tube. The A2A' IMP X2A" fluorescence excitation spectrum was observed in the wavelength region 615 - 692 nm. The origin was located at 14,542 cm-1; the vibrational frequency for the SO stretching of the A state was 859 cm-1. Dispersed fluorescence was observed in the 680 - 850 nm region. The main progressions gave vibrational frequencies of 1066 cm-1(nu)5", SO stretching), 704 cm-1 ((nu) 7)", CS stretching), and 1464 cm-1 ((nu) 4)", CH3-deformation). The results agree with ab initio calculations. Infrared absorption lines of the CH3)S radical were observed after UV photolysis of a CH3)SH/Ar (1/500) matrix at 12 K. The results yielded (nu) 1) (CH stretching) equals 2948.6, (nu) 2) (CH3)-umbrella) equals 1315.1, ((nu) 3) (CS stretching) equals 719.4, (nu) 4) approximately equals 2873, and 2(nu) 6) (CH3) rocking) equals 1154 cm-1.