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-c atalyzed 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, sep arated by a continuous and a discontinuous kinetic phase transition. A bove the discontinuous transition there is a region of near bistabilit y in which the poisoned phase is stable and the reactive phase is stro ngly metastable. This regime exists in a very narrow band of impingeme nt rates when there is no diffusion but becomes much broader when surf ace diffusion is fast. We present MC measurements of the range of the bistability when the diffusion and reaction rates are similar. The A d iffusion rate is found to affect the bistable regime dramatically. The physical origin of this effect and its relation to experiments is ana lyzed. We further quantify the effects of diffusion on this reaction b y measuring the surface lifetime and mobility of adsorbed A particles.