critical energy (threshold energy)

https://doi.org/10.1351/goldbook.C01393
A chemical reaction cannot occur, except by @Q04989@ unless the total energy available is greater than a certain energy, which is known as the critical energy, or the @T06366@.
Source:
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 162 [Terms] [Paper]