In an elementary process, a species having sufficient energy to become an activated complex, but which does not have the structure of the activated complex. If it is not inactivated by collisions it can become an activated complex and pass at once into products, after undergoing vibration.
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)
) on page 164 [Terms