Reorganization of adsorbed films by coadsorbing species
Coadsorption of CO and butane on a Pt(533) surface leads to a dynamical system in which both molecules influence the adsorption behavior of each other. Adsorbing butane on a Pt(533) surface with CO on atop step sites leads to tilting of CO molecules of at least 42 away from the surface normal and displacement along the step edge from atop to bridge sites. The tilting energy should be <20.5 kJ/mol. The tilting and displacement of CO together with the occurrence of the compressed butane phase at the same coverage at which it forms on a clean Pt (533) surface leads to the assumption that at low coverages the most probable adsorption site of butane is on the terrace planes, rotated 60° away from the step edge. This is supported by observation that butane is forced to form a compressed phase at lower coverages with respect to adsorption on a bare Pt(533) surface when CO also occupies some terrace sites. The compressed phase is suggested to consist of tilted molecules near the step edge, having two hydrogen atoms in direct contact with the surface.