Photoionization is a process in which an atom or molecule absorbs a photon of light and subsequently ejects one or more of its electrons, resulting in the formation of an ion. This phenomenon is crucial in various fields such as astrophysics, chemistry, and plasma physics. The process can be described as follows: 1. **Photon Absorption**: An atom or molecule absorbs a photon whose energy is greater than or equal to the ionization energy of the atom or molecule.
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Photoionization removes a bound electron when an atom or ion absorbs a sufficiently energetic photon. The threshold is its ionization energy. The excess photon energy becomes kinetic energy of the products; subsequent collisions can heat the gas or cause secondary ionizations. A photoionization rate and a photoionization equilibrium are distinct concepts: equilibrium also requires specified recombination and other reaction rates.