Second-derivative method: Application to vibrational spectroscopy in excited electronic states

The second-derivative method, which has been known to be useful for finding peaks overlapped in a broad band, is applied to u.v. and visible absorption bands to derive vibrational frequencies in excited electronic states of molecules in solution. By using this method, much better estimates of vibrational frequencies are possible for Franck—Condon active modes than can be made from the absorption spectrum itself. Computational procedure and the results obtained for trans-1,3,5-hexatriene, azulene, pyrazine and anthracene are described with remarks about the effectiveness and limitations of the second-derivative method.