Potential functions of N-C and C-S internal rotations and normal coordinate analyses of carbamothioic acid H₂N-CO-SCl

The structural stability of carbamothioic acid NH₂CO-SCl was investigated by DFT-B3LYP and ab initio MP2 calculations using 6-311+G** basis set. Full energy optimizations were carried out and the molecule was predicted to exist predominantly in the trans (CO and S-Cl bonds are anti to each other) conformation. From the calculations, the two-fold NH₂ barrier about the N-C bond was calculated to be about 12 kcal/mol, while, the asymmetric OCSCl barrier about the C-S bond to be about 8 kcal/mol. The vibrational frequencies of the d₀- (NH ₂COSCl) and d₂- (ND₂COSCl) deuterated species of the molecule were computed at the DFT-B3LYP level. Then vibrational assignments for the normal modes of the compound in its stable trans conformation were made on the basis of normal coordinate calculations.