KINETIC PHASE-TRANSITIONS AND BISTABILITY IN A MODEL SURFACE-REACTION .1. MONTE-CARLO SIMULATIONS

We have performed Monte Carlo simulations for a model of the surface-catalyzed 2A + B-2 --> 2AB reaction in which the surface reaction rate and the A surface diffusion rate are finite. The kinetic phase diagram for this model contains two poisoned phases and a reactive phase, separated by a continuous and a discontinuous kinetic phase transition. Above the discontinuous transition there is a region of near bistability in which the poisoned phase is stable and the reactive phase is strongly metastable. This regime exists in a very narrow band of impingement rates when there is no diffusion but becomes much broader when surface diffusion is fast. We present MC measurements of the range of the bistability when the diffusion and reaction rates are similar. The A diffusion rate is found to affect the bistable regime dramatically. The physical origin of this effect and its relation to experiments is analyzed. We further quantify the effects of diffusion on this reaction by measuring the surface lifetime and mobility of adsorbed A particles.