Band Shapes of the Electronic Spectra of Complex Molecules

Structureless bands of ultraviolet absorption spectra of hydroxypyridine derivatives in solution have been examined. It is shown that the log–normal distribution provides a convenient four-parameter empirical description of the bands and gives a much better fit than the two half-width Gaussian. The log–normal yields a resolution of overlapping bands by a method of least squares that is very satisfactory. A simple configuration-coordinate model is presented that lends some physical meaning to the parameters of the log–normal. It yields normalized third and fourth moments that are near those of the log–normal.