Structurally mixed molecular eigenstates of 2-fluoroethanol resulting from conformational isomerization

Using a newly developed method of molecular-beam, infrared-microwave double-resonance spectroscopy, we are able to measure the rotational spectrum of a single molecular eigenstate of the molecular Hamiltonian near $\text{3000\hspace{0.5em}}{\mathrm{cm}}^{\mathrm{-1}}$ of energy above the ground rovibrational state. This energy lies above the barrier to conformation isomerization in many molecules. In the $–{\mathrm{CH}}_{\mathrm{2}}\mathrm{F}$ asymmetric C–H stretch of the $\mathrm{Gg}$ conformer of 2-fluoroethanol, near $\text{2983\hspace{0.5em}}{\mathrm{cm}}^{\mathrm{-1}},$ we demonstrate the contribution of vibrational states localized around the $\mathrm{Tt}$ conformer structural minimum to the individual molecular eigenstates. The measurement demonstrates the ability of isolated molecules to use vibrational excitation to achieve geometrical rearrangement.