Fermi Resonance Variability Induced by Solute/Solvent Interaction: Phthalic Anhydride

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Abstract
The amount of Fermi resonance (F.R.) interaction between vo.p. (C=O)2 and a combination tone of phthalic anhydride varies systematically with change in the volume percent ratios of the solvents such as CHCl3/CCl4 and (CH3)2SO/CCl4. Correction for F.R. shows that vo.p. (C=O)2 decreases 5.2 cm−1 while the combination tone increases 3.2 cm−1 in going from CCl4 solution to CHCl3 solution. At 23.1 volume % CHCl3/CCl4, the bands in F.R. (1789 and 1776 cm−1) have equal intensity, and in this unique case both bands result from equal contributions from vo.p. (C=O)2 and the combination tone. The solute/solvent interaction in the (CH3)2SO/CCl4-phthalic anhydride system is even larger than that for the CHCl3/CCl4-phthalic anhydride system.