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SACHIE SAKURAI, NIKLAS MEINANDER, JAAN LAANE, Department of Chemistry, Texas A\&M University, College Station, TX 77843; TIM KLOTS, BDM Oklahoma, Bartlesville, OK 74001.
The far- and mid-infrared spectra of phthalan have been recorded and the ring-puckering and ring-flapping (butterfly) vibrations, which have fundamental frequencies of 31 and 216 cm-1 respectively have been examined in detail. These two vibrations are strongly coupled and result in complex spectra with numerous sum, difference and hot bands series. Since a one-dimensional potential energy function for the ring-puckering vibration cannot adequately account for the spectra, previous analysis of the far-infrared and dispersed fluorescence spectra were not accurate. We have utilized a two-dimensional potential energy surface along with calculated kinetic energy expansions to attain a very nice agreement between observed and calculated transition frequencies. This bicyclic ring molecule is found to be nearly planar with a small barrier to planarity (around 50 cm-1), due to the ring puckering.