Chemically limited reactions on a percolation cluster

Theoretical arguments and Monte Carlo results show that under certain circumstances, obstruction may increase the reaction rate of a binary reaction A+B→products. Near the percolation threshold, anomalous subdiffusion slows the initial encounter of the reactants, but it also slows the separation of the reactants after an unsuccessful collision. In a finite system, if the reaction probability P per collision is small enough, the recollision effect predominates and the reaction rate is enhanced slightly. As a result of this effect, as P is varied, the range of reaction rates on a percolation cluster is much smaller than the range for an unobstructed system. Furthermore, there is a crossover reaction probability PCR at which the reaction rate becomes practically independent of obstacle concentration for the entire range from the unobstructed system to the percolation threshold.