Theory of Torsion Vibrations of (CH3)2X‐Type Molecules

The torsion vibrations of (CH3)2X‐type molecules having C2v and Cs point‐group symmetry were analyzed by using a Hamiltonian that includes top—top interaction terms. The energy levels were calculated by first‐order perturbation methods and the selection rules for the infrared‐active transitions were analyzed by group theoretical arguments. Explicit expressions which have been derived for the high potential‐barrier approximation were used to discuss the torsion vibration spectrum of the (CH3)2S molecule.