ABSTRACT
This chapter emphasizes the aspects of atomic and molecular theory which are important to understanding of high-resolution laser spectroscopy of highly excited states. It is concerned with high-angular-momentum quanta carried by the electrons in atoms or the vibrations and rotations in molecules which give rise to fine-structure spectra. The chapter discusses another useful but often ignored tool for understanding the combinatorics of both the electrons in atoms and the nuclei in molecules. It explains the almost forgotten semiclassical picture which is just gaining popularity as a useful tool in understanding high-resolution spectroscopy. The chapter discusses the line shapes, cross sections, and saturation of transitions appropriate to high-resolution spectroscopy. For high-resolution spectroscopy it is important to overcome linebroadening effects, which often obscure the detailed atomic and molecular substructure which is hidden beneath the line profile in ordinary absorption spectroscopy. The chapter identifies the degeneracy of the nuclear spin levels and considers the hyperfine splitting for polyatomic molecules.
