critical energy (threshold energy) 

https://doi.org/10.1351/goldbook.C01393
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.
Source:
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 162 [Terms] [Paper]
Citation: 'critical 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 RIS BibTex EndNote
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Last revised: February 24, 2014