ANALYSIS OF TORSIONAL SPECTRA OF MOLECULES WITH 2 INTERNAL C-3V ROTORS .11. LOW-FREQUENCY VIBRATIONAL-SPECTRA, METHYL TORSIONAL POTENTIAL FUNCTIONS, AND INTERNAL-ROTATION OF ETHYL METHYL SULFIDE

The infrared and Raman spectra of gaseous ethyl methyl sulfide have been investigated below 500 cm-1. A number of torsional transitions were observed and have been assigned on the basis of an equilibrium between the gauche and high energy s-trans conformers. The asymmetric potential function for the CH2-S torsion has been calculated from observed transitions which leads to a value for the enthalpy difference between s-trans and gauche conformers of 46 ± 14 cal/mol. The values of the potential coefficients were V1 = -44.7 ± 5.7 cm-1 (-128 cal/mol); V2 = 23.7 ± 5.9 cm-1 (68 cal/mol); V3 = 1230 ± 8 cm-1 (3517 cal/mol); V6 = -124.7 ± 2.8 cm-1 (-357 cal/mol). One series of torsional transitions in the Raman spectrum and another in the infrared spectrum have been assigned to the coupled methyl torsions of gauche-ethyl methyl sulfide which lead to barrier heights for the C-CH3 and S-CH3 symmetric torsions of 3.33 and 2.05 kcal/mol, respectively. © 1979 American Chemical Society.