Results for repulsive interactions

We start with the system without B-desorption k = 0). This case is realistic for the oxidation of CO because the O atoms (B particles) are strongly bound to the metal surface and desorption does not occur at the temperatures used for this reaction. In this case the parameter Ebb does not play a role because the transition probabilities for the A and B particles depend on b/Pb and on /ca/Pa respectively. Therefore we have reduced the number of energetic parameter to two (Eaa and bb)- In the following we present all values of E fj, in /cbT units. 

In Fig. 9.16 the coverages of A and B and the production rate Rqo2 re shown as a function of Yco- We assume a large desorption rate k = 0.05 and no diffusion D = 0). For curve 1 we have Eaa = Eab = 0, which corresponds to the case of the ZGB-model incorporating A-desorption. The value of yi is not shifted by the desorption because at this point too few A particles are present. Complete coverage of the lattice by A does not occur because at every time step A particles have the chance to desorb from the surface. Both facts are in agreement with the corresponding Monte Carlo simulations [15]. 

In curve 2 we switch on the A-A interaction ( aa = 1 and Eab = 0), which corresponds to a repulsion between the A particles. Due to the repulsion the phase transition at y2 nearly disappears and we obtain a very 

Curve 3 shows the diagram for Ea = 0 and Eab = 1 The parameter Eab shifts the critical point y dramatically to larger values of Vco which means that the complete occupation of the lattice by B easily takes place. This is understandable from the fact that the A-adsorption probability is decreased by the repulsion with the B particles, which are the dominant species on the lattice. Therefore the tendency of the B particles to form large clusters is enhanced. This can be seen from Rco2 which is for Fco V2 nearly zero and rises sharply at Fco V2- 

In curve 4 we have Eaa = Eab = 1 This results in a smooth transition at y2 for the A-density (caused by Eaa) and a phase transition at y at large values of Yco (caused by Eab)- The parameter Eaa is important for large values of CaCi.c., for large values of Vco) and Eab dominates the system behaviour at large values of Cb (i-e., for small values of Vco)- 

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