STUDY OF THE CRITICAL-BEHAVIOR OF AN IRREVERSIBLE PHASE-TRANSITION IN THE A+B-]AB REACTION WITH B-DESORPTION ON A FRACTAL SURFACE

A model for the generic reaction of the type A + B --> AB on a fractal surface, in the square lattice of size L X L (L less-than-or-equal-to 300), is simulated by means of the Monte Carlo technique. The employed model, based on the Langmuir-Hinshelwood reaction mechanism, has a single parameter, namely the mole fraction of B in the gas phase (p(B)). In the absence of B desorption, there is no reactive steady state with AB production, but an irreversible phase transition (IPT) from A- to B-poisoned states at p(B) = 1/2. Nevertheless, assuming B desorption, an IPT occurs at the critical point p(cB) is-approximately-equal-to 0.5562 (L = infinity), so that for p(B) less-than-or-equal-to p(cB) the fractal becomes poisoned by A species while for p(B) > p(cB) a stationary state with AB production is found. The critical behavior of the coverages with the reactants and the rate of production are studied and the corresponding critical exponents are determined. Also the correlation length exponent is evaluated.