Ab initio calculations and vibrational spectra of CH3SC CH and CH3SC CSCH3

Methylthio- (MTE) and bis-methylthioethyne (BMTE) molecules are calculated by the SCF MO method (geometry optimization, basis set 6-31G*/MP2). The cal culated internal rotation barriers of methyl groups are 7.12 kJ/mole for MT E and 12.86 kJ/mole for BMTE (both groups are simultaneously rotated). The s-gosh-orientation of the thiomethyl fragments corresponds to a stable conf ormation of BMTE. The estimated values of the s-cis- and s-trans-barriers o f mutual rotation of SCH3 groups about the an's of the C=C bond are 13.61 a nd 12.54 kJ/mole, respectively. Conformationally sensitive MOs and vibratio n frequencies are established. An analysis of the experimental IR absorptio n and Raman spectra and the calculated vibrational spectrum makes it possib le to conclude that in the liquid phase the BMTE molecules also have an s-g osh-conformation.