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This article is about autoionization of a single atom or molecule in atomic physics. For molecular autoionization by reaction of two identical molecules (a different process studied in solution chemistry), see Molecular autoionization.

Autoionization is a process by which atoms or molecules spontaneously emit one of the shell electrons, thus going from a state with charge Z to a state with charge Z + 1, for example from an electrically neutral state to a singly ionized state.[1]

Atoms can autoionize when either two or more valence electrons are excited or one or more inner-shell electrons are missing. In the latter case, it is called the Auger effect. Molecules, in addition, can experience vibrational autoionization.[2]

Autoionizing states are usually short-lived, and thus can be described as resonances rather than normal bound states.

See also[edit]


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "auto-ionization".
  2. ^ Pratt, S.T. (2005), "Vibrational Autoionization in Polyatomic Molecules1", Annual Review of Physical Chemistry 56 (1): 281, Bibcode:2005ARPC...56..281P, doi:10.1146/annurev.physchem.56.092503.141204, PMID 15796702