The ring puckering potential function of trimethylene sulfide and trimethylene selenide

The rotational constants A,B and C are functions of the vibrational quantum numbers for the out-of-plane bending modes of trimethylene sulfide and trimethylene selenide. Infrared and microwave spectroscopy have been used to determine the dependence between these parameters. The height and shape of the barrier arising from combination of the ring bending modes is also determined. CNDO/2 calculations are used to predict the position of the hydrogen atoms of the methylene groups in trimethylene sulfide and trimethylene selenide. The four-membered rings are non-planar for several vibrational states of the ring bending modes.