HYDRODYNAMIC LIMITS FOR THE MONOMER-DIMER SURFACE-REACTION - CHEMICALDIFFUSION, WAVE-PROPAGATION, AND EQUISTABILITY

For finite adspecies mobility, the lattice-gas monomer-dimer (A+B-2) s urface reaction model exhibits a discontinuous transition from a stabl e reactive steady state to a stable A-poisoned steady state, as the im pingement rate P-A for A increases above a critical value P. The reac tive (poisoned) state is metastable for P-A just above (below) P. Inc reasing the surface mobility of A enhances metastability, leading to b istability 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 becoming the equistability point for the tw o states. This hydrodynamic regime can be described by reaction-diffus ion equations (RDE's). However, for finite reaction rates, mixed adlay ers of A and B are formed, resulting in a coverage-dependent and tenso rial nature to chemical diffusion (even in the absence of interactions beyond site blocking). For equal mobility of adsorbed A and B, and fi nite reaction rate, the prediction for P from such RDE's, incorporati ng the appropriate description of chemical diffusion, is shown to coin cide with that from kinetic Monte Carlo simulations for the lattice-ga s model in the regime of high mobility. Behavior for this special case is compared with that for various other prescriptions of mobility, fo r both finite and infinite reaction rates.