This study deals with the dynamic interaction of CO with the bare Ru(0001), the fully hydrogen- and fully CO-covered ruthenium surface. Molecular beam techniques are applied to investigate the potential energy surface of the ruthenium CO interaction and the chemically modified surfaces. The clean surface shows all properties of a deep uniform chemisorption well with a strong rotational anisotropy. The strong chemically attractive interaction can be diminished by CO adsorption, which leads to zero sticking, even at translational energies as high as 1.2 eV. The angular distribution shows a substantial broadening compared to the clean surface. As shown recently, in the case of hydrogen, CO adsorption turns into an activated process with the atop position being the only available adsorption site. Scattering CO molecules from the hydrogen-covered surface leads to very narrow angular distributions. The collisions are mainly quasi-elastic.