Prepairing mechanism desorption kinetics

Believing that a concerted mechanism was not possible, Sinniah et al. [33] considered alternatives. They were particularly concerned with a prepairing mechanism, in which H atoms are paired up on adjacent sites due to an (unspecified) attractive interaction. This would easily rationalize first-order kinetics because the desorption rate would depend on the density of correlated pairs of H atoms, rather than the probability for two uncorrelated atoms to be on adjacent sites. They performed an isotopic mixing experiment... 

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