Chapter 2 - Pathways of Molecular Excitation and Deactivation

Abstract

The possible electron distributions defining the molecular orbitals and the energy levels of molecules in their ground and excited states are given by the approximate solutions of a generalized Schröodinger equation. The latter takes into account the electrostatic attractions and repulsions of protons and electrons, inter-nuclear vibrations, and the rotational movement of molecules as well as magnetic interactions because of electron and nuclear spins and orbital motion. Molecular orbitals can contain no more than two electrons. A transition between the two states of a molecule corresponds to the movement of one electron from one orbital to another. This chapter explains the pathways of molecular deactivation. Because an electron has spin angular momentum, and because moving charges generate magnetic fields, an electron has a magnetic moment, which arises from its spin. Similarly, an electron with orbital angular momentum is a circulating current, also generating a magnetic moment. The strength of the coupling and its effect on the energy levels of the molecule, depend on the relative orientation of the two angular momenta.