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The Laser Raman spectra of CH3CSNH2, CH3CSND2, CD3CSNH2, CD3CSND2, CH3CSONH2, CH3CSOND2, CD3CSONH2, and CD3CSOND2 have been measured in the solid state. A normal coordinate analysis has been carried out for the mentioned compounds using the Wilson GF matrix method. The Urey—Bradley-force field has been used in calculating the A′-vibrations; some additional general valence force constants had to be adopted in calculating the A′-vibrations of thioacetamide. In the refinement of the force constants much attention is given to the observed 13C and 15N frequency shifts, which have been obtained previously by i.r. measurements of the corresponding thioacetamides and thioacetamide-S-oxides. Potential energy distributions are given in order to characterize the normal vibrations. The double bond character of the CN bond in thioacetamide is higher than in acetamide, as is indicated by the value of the stretching force constants. The barrier to internal rotation around the CN bond in thioacetamide is evaluated from the torsional force constants assuming sinusoidal potential shape, and is found to be 33·7 kcal/mol for the crystal, and 26 kcal/mol for the solutions spectra. On comparing the force constants of thioacetamide and its S-oxide it seems that the Urey—Bradley force field is transferable for thioamides and thioamide-S-monoxides as well. The force field obtained by the procedure proposed by Becher and Mattes gives no satisfactory results in fitting the data of all isotopically substituted compounds.