INFRARED-MICROWAVE DOUBLE-RESONANCE AS A DOORWAY TO DARK STATES IN A PERTURBED SPECTRUM: THE $10 \mu$m SPECTRUM OF 2-FLUOROETHANOL
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Date
1993
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Publisher
Ohio State University
Abstract
The infrared spectra of the $C-O$ and $C-F$ stretches of the Gg comformer of 2-fluoroethanol have been measured at 2 MHz resolution using an electric-resonance optothermal spectrometer and a tunable microwave-sideband $CO_{2}$ laser. The $C-O$ stretching band is well described by an asymmetrical top Hamiltonian with a and b type selection rules and origin at $1089.07 cm^{-1}$. The $4_{13}$ upper state is split into a doublet through its interaction with a $J=4$ level of a background vibration. The small magnitude of the coupling matrix element (- 20 MHz) suggests that the interaction is extremely high-order, perhaps involving a vibrational state arising from another conformer. To assess the nature of the background or dark vibrational state, microwave-infrared double resonance is being used to measure the microwave spectrum of the dark state. The observed microwave transitions originate On one of the two components of the 413 doublet. At present, two such microwave transitions have been found. These observations have not yet allowed us to uniquely specify the rotational constants of the dark state, nor have we been able to definitely determine the $K_{a}$ or $K_{c}$ quantum numbers of the rotational level of the dark state interacting with the 413 level of the $C-O$ stretch. Efforts are also underway to assign the $C-F$ stretching band near $1038.5 cm^{-1}.$
Description
Author Institution: Department of Chemistry, Cornell University; Molecular Physics Division, National Institute of Standards and Technology