Laser-ablated scandium, yttrium, and lanthanum atoms were reacted with CS2 and OCS molecules in an argon matrix. Products of the type SMCX and S-M(eta(2)-CX) ( X = S or O) were formed on sample deposition. Photolysis favored the S-M(eta(2)-CX) complex, while annealing increased the more stable SMCX isomer. Product absorptions are identified by density-functional frequency calculations and isotopic substitutions. This work reports the first vibrational spectroscopic characterization of Sc, Y, and La reaction products with CS2 and OCS and the subsequent interconversion between SMCX and S-M(eta(2)-CX) structural isomers.