[foh-toh-ahy-uh-nuh-zey-shuh
n] 
| the phenomenon in which the absorption of electromagnetic radiation by an atom in a gas induces the atom to emit a bound electron and thereby become ionized. |
photoionization
the interaction of electromagnetic radiation with matter resulting in the dissociation of that matter into electrically charged particles. The simplest example, the photoelectric effect (q.v.), occurs when light shines on a piece of metal, causing the ejection of electrons. Another category of photo-ionization involves the disruption of covalent chemical bonds, producing positively and negatively charged fragments; such a reaction is often called the primary process of a photochemical reaction (q.v.).
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