Rates of molecular desoption from solid surfaces: Adsorption site dependence for CO on Ni(100)

The role of different adsorption sites on the rate of desorption of CO from Ni(100) surfaces has been studied using the classical stochastic diffusion theory (CSDT) formulation. The microscopic parameters of the system (force constants and bond energies) have been obtained form ab initio cluster calculation (Ni₁₄ and Ni₂₀ clusters) with generalized valence bond wavefunctions. In good agreement with experiment, our calculations show that desorption occurs in two temperature ranges: 400-600 K and 150-250 K. In the higher-temperature range, the one-fold and two-fold sites are primarily responsible for the desorption rate, while for the lower-temperature range, the four-fold (weakest binding site) is dominant (experimentally achieved by poisoning the surface with S).