PRECURSOR AND OVERLAYER STRUCTURAL EFFECTS IN THE INTERACTION OF CO WITH NI(110)

We present isothermal measurements of CO adsorption and desorption rates on Ni(110) that reveal clearly the participation of a precursor state in both processes at all coverages. Accounting for its effect allows activation energies and preexponential factors to be determined that are specific to the coverage regimes where c(8 x 2), c(4 x 2), and (2 x 1) ordered structures are known to form at low temperatures. The preexponential factors include a significant contribution attributable to relaxation of the adsorbed layer from one structure to another as desorption proceeds, and the relaxation process is also manifested in the relationship between measured activation energies and integral heats of adsorption. The results have general implications for adsorption systems involving series of ordered overlayers.