The Widespread Applicability of Lognormal Curves for the Description of Absorption Spectra

Abstract

We have fitted over 160 electronic absorption spectra of over 95 aromatic compounds and some other substances with lognormal distribution curves to evaluate the shapes of the bands. The compounds include simple benzene derivatives, phenols, anilines, benzaldehyde, benzoic acid, nitrobenzene, and potassium permanganate. The well-defined n-π* transitions of acetone, benzaldehyde, nitrobenzene, and pyrazine are included. Effects of solvents have been studied in a number of cases. The fitting of absorption bands with lognormal curves is compared with resolution with Gaussian curves or with other types of skewed Gaussian curves. We conclude that the lognormal curve provides an excellent approximation to the shapes of spectral bands in aromatic as well as many other organic and inorganic compounds. The ability to analyze complex spectra by resolution with lognormal curves may be usefully applied in a number of ways.