Title: auto-ionization
Long Title: IUPAC Gold Book - auto-ionization
DOI: 10.1351/goldbook.A00526
Status: current

Definition
This occurs when an internally supra-excited atom or molecular moiety loses an electron spontaneously without further interaction with an energy source. (The state of the atom or molecular moiety is known as a pre-ionization state.)

Related Terms
- ionization: https://goldbook.iupac.org//terms/view/I03183
- moiety: https://goldbook.iupac.org//terms/view/M03968

Sources
- Orange Book, 2nd ed., p. 206 (https://media.iupac.org/publications/analytical_compendium/)
- PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1547 (https://doi.org/10.1351/pac199163101541)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00526/html
- json: https://goldbook.iupac.org/terms/view/A00526/json
- xml: https://goldbook.iupac.org/terms/view/A00526/xml

Citation: Citation: 'auto-ionization' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.A00526
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Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-07-26T04:52:00+00:00