Analysis of torsional spectra of molecules with two internal C3v rotors. X.a) Low frequency vibrational spectra, methyl torsional potential functions, and internal rotation of ethylmethylether (‐d0 and ‐d3)

The vibrational spectra of gaseous ethylmethylether C2H5OCH3 and C2H5OCD3 have been investigated at high resolution below 500 cm−1. Considerable torsional data are reported and assigned on the basis of an equilibrium between the s‐trans and the high energy gauche conformers. Asymmetric potential functions for the CH2–O torsions have been calculated from observed transitions, leading to values for the enthalpy difference between the gauche and s‐trans conformers of 1.36 and 1.28 kcal/mole, respectively, for the ‐d0 and ‐d3 compounds. Analysis of the transitions above 130 cm−1 indicates that the two methyl rotors have strongly coupled torsional vibrations in both compounds, and that previous assignments are insufficient for explaining the data. Transitions due to the methyl torsions of the molecules in the first excited states of the asymmetric CH2–O torsions are reported; also, some weak bands have been assigned tentatively as methyl torsions of gauche‐ethylmethylether. Torsional potential functions and ba...