Far-Infrared Spectra and Two-Dimensional Potential Energy Surfaces Involving the Ring-Puckering Vibration of 2,5-Dihydrothiophene
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The far-infrared spectra of 2,5-dihydrothiophene not only show the principal ring-puckering series in the 87-127 cm-1 region but also possess two sideband series arising from the ring-twisting first and second excited states. A third series arises from puckering transitions in the excited state of the ν9(Ag) in-plane ring angle bending vibration, which occurs at 509.9 cm-1. The ring-puckering levels in the ν9 excited state are also confirmed by observed sum, difference, and hot bands. Observed double-quantum transitions confirm many of these assignments. Each of the four series can be fit well with a one-dimensional single minimum potential function possessing positive quartic and quadratic terms. Two-dimensional potential energy surfaces were also calculated to assess the interaction of the ring-puckering with the ring-twisting and in-plane ring bending modes. The twisting is anticooperative, raising die energy of the puckering process, while the inplane ring bending is cooperative, facilitating the puckering motion.
author list (cited authors)
Klots, T., Lee, S., & Laane, J.