VIBRATIONAL-SPECTRA OF MONOTHIOCARBAMATES .2. IR AND RAMAN-SPECTRA, VIBRATIONAL ASSIGNMENT, CONFORMATIONAL-ANALYSIS AND AB-INITIO CALCULATIONS OF S-METHYL-N, N-DIMETHYLTHIOCARBAMATE

The IR (3200-30 cm(-1)) spectra have been recorded for S-methyl-N,N-di methylthiocarbamate, (CH3)(2)NC(O)SCH3, and its isotopomers, S-d(3), N -d(6) and N-d(9), for the gas and liquid. Additionally, the Raman spec tra (3200-10 cm(-1)) for the solid and liquid, with qualitative depola rization ratios, have been obtained for all the isotopes. These data a re interpreted on the basis that the s-cis conformer (the S-methyl gro up oriented cis to the carbonyl group) with C,symmetry is the only for m existing in all three phases for this molecule. A complete vibration al assignment proposed for the -d(0) molecule is facilitated by the av ailability of spectral data for five different isotopomers. A normal c oordinate analysis has been carried out utilizing ab initio calculatio ns with the 3-21G basis set. The potential energy distributions and a b initio calculated frequencies have allowed a clarification of some o f the corresponding results obtained from experiment. Structural optim izations and potential surface scan have also been carried out by ab i nitio calculations with the 3-21G basis set. These results are compar ed with some previous studies on this molecule as well as on similar m olecules.