Hydrodynamic limits for the monomer-dimer surface reaction: Chemical diffusion, wave propagation, and equistability

Abstract

For finite adspecies mobility, the lattice-gas monomer-dimer (A+B{sub 2}) surface reaction model exhibits a discontinuous transition from a stable reactive steady state to a stable A-poisoned steady state, as the impingement rate P{sub A} for A increases above a critical value P{sup {asterisk}}. The reactive (poisoned) state is metastable for P{sub A} just above (below) P{sup {asterisk}}. Increasing the surface mobility of A enhances metastability, leading to bistability in the limit of high mobility. In the bistable region, the more stable state displaces the less stable one separated from it by a planar interface, with P{sup {asterisk}} becoming the equistability point for the two states. This hydrodynamic regime can be described by reaction-diffusion equations (RDE{close_quote}s). However, for finite reaction rates, mixed adlayers of A and B are formed, resulting in a coverage-dependent and tensorial nature to chemical diffusion (even in the absence of interactions beyond site blocking). For equal mobility of adsorbed A and B, and finite reaction rate, the prediction for P{sup {asterisk}} from such RDE{close_quote}s, incorporating the appropriate description of chemical diffusion, is shown to coincide with that from kinetic Monte Carlo simulations for the lattice-gas model in the regime of high mobility. Behavior for this special casemore » is compared with that for various other prescriptions of mobility, for both finite and infinite reaction rates. {copyright} {ital 1998} {ital The American Physical Society}« less