Title: cage
Long Title: IUPAC Gold Book - cage
DOI: 10.1351/goldbook.C00769
Status: current

Definition
An aggregate of molecules, generally in the condensed phase, that surrounds the fragments formed, for example, by thermal or photochemical dissociation. Because the cage hinders the separation of the fragments by diffusion, they may preferentially react with one another ('cage effect') but not necessarily to reform the precursor species. For example: 

Related Terms
- cage effect: https://goldbook.iupac.org/terms/view/C00771
- diffusion: https://goldbook.iupac.org/terms/view/D01716
- dissociation: https://goldbook.iupac.org/terms/view/D01801
- geminate recombination: https://goldbook.iupac.org/terms/view/G02603

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1091 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C00769/html
- json: https://goldbook.iupac.org/terms/view/C00769/json
- xml: https://goldbook.iupac.org/terms/view/C00769/xml

Citation: Citation: 'cage' 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.C00769
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
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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: 2026-06-29T16:23:07+00:00