Knowledge Bank

We have measured the high resolution (5 MHz) infrared spectrum of the asymmetric$-CH2$(F) stretch of 2-fluoroethanol $(HO-CH2-CH2F)$ near $2980cm-1$ 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 $1000cm-1$. 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 $Ka$-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.