ABSTRACT
The charge distribution of an atom or molecule provides a handle by which electromagnetic radiation interacts with matter and causes spectroscopic transitions. As discussed in the previous chapter, light consists of oscillating electric and magnetic fields. These fields can exert torques on the electric and magnetic multipoles of molecules, causing energy to be absorbed by matter. Conversely, oscillations in the charge distribution of a molecule result in the emission of electromagnetic radiation. The reciprocity of these two physical phenomena, oscillating charge distributions and electromagnetic radiation, is an elegant example of symmetry in the laws of nature.
