1. A study has been made of the Raman and IR spectra of triethylarsine sulfide (TEAS), in the solid and liquid states, in various solvents, and at various temperatures. 2. In the solid state, TEAS appears as an isomer with C3 symmetry, the three C2H3 groups being gauche-oriented with respect to the As=S bond. In the molten form, and in solutions, the compound appears as an equilibrium mixture of three isomers with C2, Cs, and C3 symmetries. 3. Frequencies and normal vibration modes have been calculated for these three conformers of the TEAS molecule.