AB-INITIO STUDY OF MOLECULAR-CONFORMATIONS, GROUND-STATE FORCE-FIELD AND VIBRATIONAL-SPECTRA OF S-METHYL DITHIOCARBAMATE

The molecular conformations, ground state molecular vibrations and force field of S-methyl dithiocarbamate (SMDTC) have been studied using the HF/6-31G* method of ab initio quantum chemistry. It is found that SMDTC as a free molecule exists predominantly as the Z conformer. The stability of SMDTC as the E conformer in the solid state is attributed to packing forces and intermolecular hydrogen bonding. Normal coordinate analyses have been carried out for SMDTC and its N- and C-deuterated isotopomers and the previous vibrational assignments have been critically examined and some revisions made. The ground state effective force field of SMDTC has been obtained using the RECOVES procedure suggested by us recently. The RECOVES-HF/B-31G* force constants for SMDTC are found to be highly satisfactory for predicting the vibrational frequencies of the deuterated isotopomers of SMDTC. The theoretical infrared and Raman intensities of the normal modes together with the qualitative experimental infrared band intensities are presented. The predicted relative infrared intensities compare well qualitatively with the experiment for the matrix isolated species.