OP-II-3

PP-III-20take into account own size of molecules and its chemical structure we involve infinitystrong repulsive interactions between adsorbed nearest-neighbor dimers. Adsorptionprocess is simulated through a grand canonical ensemble. Parameters of the modelare temperature, chemical potential, value of difference between adsorption heat ontwo site of adsorption and one site, size and type of lattice. Model has beeninvestigated with the Monte Carlo method and the transfer-matrix technique.We have plotted isotherms and coverage curves for all types of lattices, on whichone could see well defined plateaus. These plateaus correspond to ordered phasesappeared in the system (there are phases consisting of only dimers adsorbed on onesite, only two sites and complex structures with both types of adsorbed dimers). Foreach ordered structure unique orderparameter is defined, which is equal to 1 ifcorresponded phase takes place in thesystem and equal to 0 otherwise. Wehave calculated different thermodynamicquantities such as entropy, differentialheat of adsorption, adsorption energy etc.Phase diagrams have been plotted foreach type of lattices. Fig. 2 shows phasediagram of dimers on square lattice.Fig. 2. Phase diagram of dimersadsorbed on square lattice.From obtained data we conclude thatsurface geometry has significant influence on ordered phase in similar systems. It isinteresting that complex structures, formed by both vertical and horizontal orienteddimers, appear only on triangular and honeycomb lattices, but not on square one. Inaddition phenomenon of nonmonotonic changing of coverage takes place in oursystem (only on triangular and honeycomb lattices). It means when pressure in thegas phase growths the amount of empty adsorption sites growths too. We cansuppose that all these observed features of dimer adlayer are inherent in realadsorption systems.References[1]. Steele, W. A. The Interaction of Gases with Solid Surfaces // Pergamon Press: Oxford, 1974.[2]. Su G. J., Zhang H. M., Wan L. J., Bai C. L., Wandlowski T. J.Phys.Chem. B. 2004. v.108. p.1931.[3]. Fefelov V.F., Gorbunov V.A. Myshlyavtsev A.V., Myshlyavtseva M.D. Chem. Eng. J. (2009) v.154 p.107.[4]. Fefelov V.F., Gorbunov V.A. Myshlyavtsev A.V., Myshlyavtseva M.D. App. Surf. Sci. (2009)doi:10.1016/j.apsusc.2009.12.065[5]. Roma F., Ramirez-Pastor A.J., Riccardo J.L. Langmuir (2003) v.19 p.6770.477