Electronic States

Abstract

Having presented in Chaps. 9 and 10 a treatment of the rotational and rotational-vibrational spectra of molecules, which lie in the microwave and the infra-red spectral regions, respectively, we turn in this and in the following chapter to electronic transitions in molecules, and thus to band spectra in the general sense. These spectra are observed in the near infra-red, in the visible, and in the ultraviolet spectral ranges, and consist of a very large number of lines with a structure which is often difficult to analyze. When observed with a spectrometer having a limited resolution, they appear as structureless, band-like spectra; hence the name ‘band spectrum’. In this chapter, we present the fundamentals needed to understand the molecular quantum numbers. Following another detailed treatment of diatomic molecules in Sect. 13.3, we give a preview of the subject for larger molecules in Sect. 13.4.