Evaluation of UV-VIS Spectral Bands

Abstract

In Chapter 2, the basic theoretical correlations of electronic excitation spectra were briefly discussed and items of important molecular physical information which can be obtained from these spectra were pointed out. The relevant parameters are the absorption maxima corresponding to the term differences (= excitation energies) from the ground state; the intensities, given in $\varepsilon _\lambda$ which correlate with the oscillator strength f; and the structure of the absorption bands traceable to overlapping of the vibrational excitation structure. Exact experimental data are required for correlation with theoretical calculations. However, UV-VIS absorption spectra measured in solution are often unstructured and have only weakly characterized shoulders which frequently make a clear assignment of excitation energies $E = hc\; \times \;\tilde v_{max}$ difficult or even impossible. A determination of the oscillator strength, f, from Eq. (5) is unreliable in these cases. For that reason, some important complementary assessments will be briefly described in this chapter.