General Features of Early Potential Energy Barriers for Exothermic Reactions

5 General Features of Early Potential Energy Barriers for Exothermic Reactions 

Exothermic reactions release energy, and initially this energy resides in the products. The conclusions are independent of whether the attacking atom, A, is light or heavy 

In the exit valley C separates from B when A is still far from B. Even when C has separated from B by a very considerable extent, the AB distance remains large compared to its equilibrium internuclear distance. The reaction energy is released as the new bond is forming. Repulsion between B and C cause B and C to recoil from each other as they separate, and B is propelled towards the approaching A as the AB bond is forming. 

Reactions on attractive surfaces with early barriers are promoted by high translational energy in the reactants, with vibrational energy playing a minor role. Selective enhancement by translational energy is easiest when there is a straight run up the entrance valley to the critical configuration. 

Vibrational energy is less important, because high vibrational energy would encourage the reaction unit to hit the barrier wall perpendicular to the reaction coordinate at the end of the straight run up the entrance valley, from which it would be bounced back down the entrance valley. 

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GENERAL FEATURES OF EARLY POTENTIAL ENERGY BARRIERS FOR EXOTHERMIC REACTIONS... 

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