Relativistic Wave Equations
In order to provide a quantitative basis to the study of atomic spectra, discussed in the next chapters of this book, it is first necessary to present a thorough study of the relativistic equations for atomic particles, with particular emphasis on the Dirac equation for the electron. In this chapter we will see how it is possible to describe, within quantum mechanics, the dynamical properties of a relativistic particle, either free or moving in a stationary electromagnetic field. Once an appropriate matrix formalism will be introduced, a number of physical consequences will naturally follow. We note that elementary treatises of atomic spectroscopy often introduce such physical consequences (e.g. electron spin, spin-orbit interaction, etc.) in a phenomenological way.