Detailed balancing and quasi-equilibrium in the adsorption of hydrogen on copper

The apparent equilibrium relationship between adsorption and desorption distributions measured in recent molecular beam experiments is discussed. Through an equilibrium synthesis and the application of detailed balancing, the energy and angle dependence of the dissociative adsorption probability of hydrogen on copper is shown to predict the non-cosine angular distributions of desorption. In a similar construction, the velocity distribution of H 2 desorbing from nickel predicts the peaked desorption angle distributions observed. The implications of the apparent local equilibrium and detailed balancing at low pressure on the mechanism of surface catalyzed isotopic exchange and on the dynamics of chemical processes on surfaces are discussed.