Chapter 3 - The Structure of Matter

Abstract

This chapter focuses on the electronic and nuclear structure of matter in each type of structure that relates to the optical spectroscopies used for diagnostics. Electrons are assumed to respond instantaneously to any change in nuclear motion because they are 103-104 times lighter than atomic nuclei. In the Born-Oppenheimer approximation, the electronic energy levels are determined with the nuclear positions fixed and parameterized. The nuclear motion and structure are then determined by using these calculated electronic energy curves. The total energy of any state is the sum of the electronic and nuclear motion energy, and transitions between these states can be considered as separate transitions between electronic and nuclear motion states. Coupling between electronic and nuclear motion cannot be totally ignored, as is seen by some transition selection rules and resonance effects in spectroscopy and by electron-phonon coupling in solids; these effects are not very important in diagnostics.