Solvent Effects on the Intensities of Forbidden Bands of Molecules. Absorption Spectra of Acetone and Cyclopentanone

The near ultraviolet absorption spectra of acetone and cyclopentanone have been studied in various fluid solutions at room temperature. The intensity enhancements observed are ascribed to perturbation of dispersion forces between solute and solvent molecules. The results are parallel to those of the Ham effect in benzene. No correlation was found between the intensity increments and solvent polarities. This is at variance with the correlation that has been reported in the S1(Lb)–S0 transition spectra of pyrene and coronene.