Complex barrier responses, examples

These predictions are consistent with the experimental value of 58 kcal/ mol for the activation barrier to desorption, but it permits only a small barrier for the reverse adsorption reaction. Nachtigall et al. [75] pointed out that if there is a substantial activation barrier to adsorption, these calculations could not be consistent with desorption from a prepaired state. They suggested that a more complex, multistep mechanism might be responsible for desorption. For example, they drew an analogy with gas-phase elimination of H2 from disilane, in which the 1,1-elimination mechanism has a lower activation barrier than the 1,2-elimination [75]. They suggested that desorption may occur by a 1,2-hydrogen shift (to form a dihydride) followed by 1,1-elimination (desorption of the dihydride). This speculation was supported... 

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