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.