Lateral interaction and CO adlayer structures on the Pt(1 1 1) surface

We have revisited the structures for CO films adsorbed on the Pt(1 1 1) surface and simulate the diffraction patterns. In particular, we suggest alternative placement of the CO molecules in the unit cell of the c(4×2) structure for CO on Pt(1 1 1) at θ=0.5. To correctly explain the LEED pattern, found from experiment at θ=0.5, the cell ultimately should be asymmetric. This agrees with recent STM results for similar CO structures on Ni(1 1 1). Parameters of the lateral interaction, evaluated from the Monte-Carlo simulations, are in excellent agreement with recent first-principle calculations. Formation of the stable CO adlayer structures on Pt(1 1 1) appears to be dominated by a superposition of the dipole–dipole and indirect interactions, which provide the attraction between the molecules at a characteristic spacing of a√3. Trio interactions are also found to be important and may originate from characteristic pairs of molecules in adsorption sites of different types.