Potential energy curve on the

On the other hand, in the Frumkin-Temkin case. k2 varies with potential. The reason for this can be seen in Fig. 7.75, where one sees potential energy (p.e.) curves for the surface recombination reaction of two adsorbed H atoms in close proximity reacting to form H2, which is regarded as having a negligible heat of adsorption. The potential energy curve on the left is that for the oscillations of a single adsorbed H. It combines with another similar adsorbed H (p.e. curve not shown) to form the H2. 

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