POSSIBLE SIGNATURES OF CONFORMATIONAL ISOMERIZATION IN THE HIGH RESOLUTION INFRARED SPECTRUM OF 2-FLUOROETHANOL
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Date
1997
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Ohio State University
Abstract
We have measured the high resolution (5 MHz) infrared spectrum of the asymmetric$-CH_{2}$(F) stretch of 2-fluoroethanol $(HO-CH_{2}-CH_{2}F)$ near $2980 cm^{-1}$ using an electric-resonance optothermal molecular beam spectrometer. The infrared spectrum has been assigned using microwave-infrared double-resonance spectroscopy techniques. The infrared spectrum originates in rotational level of the most stable conformer, denoted $Gg^{\prime}$, where both internal rotors (C-C and C-O) are is a gauche conformation. The barrier to conformational isomerization is approximately $1000 cm^{-1}$. Above conformations are accessible, Tt and Tg. Two features of the infrared spectrum may indicate conformational isomerization following excitation of the C-H stretch: 1) The degeneracy of the two $Gg^{\prime}$ enantiomers is lifted in the infrared spectrum. For 2-fluoroethanol, the degeneracy is lifted only when highly torsionally excited states, or states from the Tt conformation, are involved in the dynamics. 2) There is a strong correlation between rotational states assigned to separate levels of near-degenerate $K_{a}$-asymmetry doublets indicating energy flow between these slates. These properties of the single-photon infrared spectrum are discussed in the context of subsequent infrared-microwave double-resonance spectroscopy measurements which unambiguously demonstrate conformational isomerization following C-H stretch excitation.
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Author Institution: Department of Chemistry, University of Virginia