= Photoionization
{title2=$h\nu\geq E_{\rm bind}$}
<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.
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