Vibration–rotation interactions and ring-puckering potential function in trimethylene sulphone

Abstract

The microwave spectrum of trimethylene sulphone has been studied in the ground and five vibrational excited states of the ring-puckering vibration. Very large deviations from the rigid rotor behavior were observed for the lowest pair of states. These perturbations resulted from a strong Coriolis coupling between them and have been analyzed using a reduced axis system Hamiltonian. The energy separation between the v=0 and v=1 levels has been determined from this analysis to be of 0.9106±0.0004 cm−1. Small deviations from rigid rotor spectrum were observed for the v=2 to v=5 ring-puckering states that were found to fit semirigid rotor theory where the quartic centrifugal distortion constants account for the vibration–rotation interaction effects. From the variation of the rotational constants and the vibrational separation between v=0 and v=1 states, a reduced ring-puckering potential function has been determined to be V(X)=6.62(X4−9.22X2), which gives a barrier to the planar configuration of 140±35 cm−1. With this potential function the vibration–rotation interaction effects observed for states v=2 to v=5 have been interpreted. Considerations about the ring conformation and the dynamics of the ring-puckering motion have also been made. The μa component of the electric dipole moment has been determined to be 4.8 D.