The harmonic force field of thioacetamide has been obtained by Hartree-Fock level ab initio calculations using the 4-31G(d) basis set. The force constants have been scaled to reproduce the infrared fundamental bands of argon matrix isolated CH(3)CSN2(H) and C3(D)CSNH(2). Normal coordinate calculations based on the scaled force field suggested the co-presence of cis-CH3CSNHD and rrnns-CH3CSNHD in the infrared spectrum measured for CH3CSND2. The prediction of the fundamental bands was made for CD3CSND2, cis-CD3CSNHD and rrans-CD3CSNHD. (C) 2000 Elsevier Science B.V. All rights reserved.56610351044