The influence of particle bombardment on surface reactivity is examined by using the reaction of CO on the Ni(111) surface as a model system. Thermal desorption studies shows that a large amount of residual CO may be deposited on the surface during ion bombardment. An appreciable amount of oxygen can be produced on the surface by collision-induced CO dissociation. A new dlesorption state of CO is also formed. The activation energy for CO desorption from this new state is estimated to be about 90 kJ/mol, which corresponds to a decrease of the C-Ni bond energy of 25 – 30 kJ/mol as the sample evolves from a smooth to a damaged state. The dipole-dipole repulsion is present between CO molecules adsorbed on the ion-bombarded surface, which causes CO to desorb at a lower temperature for higher CO exposures. Under similar bombardment conditions, the sticking probability of CO on the bombarded surface decreases with decreasing momentum of the impinging particle.