Study of Fermi resonance by the method of solvent variation

Abstract

A method of determining the Fermi resonance parameters and of confirming the nature of the phenomenon in complex molecules is presented. It is based on the determination of the ratio of the intensities R and the frequency separation Δ of the two components of a Fermi doublet in a wide series of solvents. A plot of R vs. Δ gives an experimental curve which can generally be fitted by a theoretical curve using as adjustable parameters the Fermi coupling coefficient W and the ratio of intensities of the unperturbed transitions R 0, assumed to be constant in all solvents. The method is tested in molecules in which Fermi resonance is well established. The Fermi Resonance parameters W and Δ 0 are determined in p-benzoquinone, cyclopentanone, benzoyl chloride and ethylene carbonate.