Term: critical energy (threshold energy)
https://doi.org/10.1351/goldbook.C01393

Definition:
A chemical reaction cannot occur, except by quantum-mechanical tunnelling unless the total energy available is greater than a certain energy, which is known as the critical energy, or the threshold energy.

Related Terms:
1) quantum-mechanical tunnelling (http://doi.org/10.1351/goldbook.Q04989).
2) threshold energy (http://doi.org/10.1351/goldbook.T06366).

Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 162 (https://doi.org/10.1351/pac199668010149)

Citation: 'critical energy (threshold energy)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01393

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