FAR-INFRARED SPECTRA AND TWO-DIMENSIONAL POTENTIAL ENERGY SURFCES FOR THE OUT-OF-PLANE RING VIBRATIONS OF CYCLOPENTANONE IN ITS $S_{0}$ AND $S_{1} (n,\pi^{*})$ ELECTRONIC STATES

Author Institution: Department of Chemistry, Texas A\&M UniversityThe far-infrared spectra of cyclopentanone has been reexamined. In addition to the ring bending series previously observed in the $80-100 cm^{-1}$ region, ring-twisting bands ($200-240 cm^{-1}$), bend-twist sum bands ($305-335 cm^{-1})$, and bend-twist difference bands were also detected for the first time. From this data a two dimensional potential energy surface with a barrier to planarity of $1408 cm^{-1}$ and a barrier to pseudorotation of 1$358 cm^{-1}$ was determined. This same surface yields calculated frequencies in good agreement for not only the undeuterated cyclopentanone, but also for four isotopomers. In addition to determining the potential energy surface for the $S_{0}$ electronic ground state, we have also utilized our previously reported fluorescence excitation spectra to determine the corresponding potential energy surface of the $S_{1}(n,\Pi^{*})$ electronic excited state. The barrier to planarity in the $S_{1}$ stated is $1273 cm^{-1}$ while the barrier to pseudorotation has been reduced substantially to $850 cm^{-1}$