critical energy (threshold energy)
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@.
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 162 [Terms] [Paper]