Photochemical principles

This chapter provides an overview of photochemistry. Life on Earth depends, both directly and indirectly, on the influence that light has on chemistry. Interactions of light with matter make up the subject of photochemistry. If there is one essential feature of photochemistry, it is probably the way in which excited states of atoms or molecules play a part in the processes occurring. The excited states of most concern to the photochemist are those in which the electrons have become distributed into a higher energy arrangement; the species are thus said to be electronically excited. The chapter then looks at the nature of light; wave mechanics and quantum numbers; the selection rules for optical absorption; the laws of photochemistry; and intramolecular energy transfer.