[Jack E/NJ]

"Limitations of the idea of Arrhenius activation energy---Both the Arrhenius activation energy and the rate constant k are ***experimentally*** determined, and represent macroscopic reaction-specific parameters that are not simply related to threshold energies and the success of individual collisions at the molecular level. Consider a particular collision (an elementary reaction) between molecules A and B. The collision angle, the relative translational energy, the internal (particularly vibrational) energy will all determine the chance that the collision will produce a product molecule AB. Macroscopic measurements of E and k are the result of many individual collisions with differing collision parameters. To probe reaction rates at molecular level, ***experiments are conducted under near-collisional conditions*** and this subject is often called molecular reaction dynamics."

Emphasis added in triple asterisks. Heat it up, Henry! 8^)

Jack E/NJ