THE MECHANISM OF STICKING TRAPPING AND DIRECT DISSOCIATION OF CARBON-MONOXIDE ON CU(110)

Carbon monoxide has been scattered from clean and sulphur covered Cu(110) surfaces with translational energies in the range 80 < E < 350 meV. At a surface temperature Ts = 700 K, the direct-inelastic (DI) and sticking-trapping (ST) channels could be clearly identified and separated in the scattered angular distributions. The behaviour of the DI channel as a function of beam energy E and incident angle θ adhere surprisingly well to the predictions of a simple hard cube model. The apparent intensitivity of the DI channel to an attractive chemisorption potential is also evident in scattering experiments from a sulphur covered surface. Adsorbed sulphur, however, causes a significant decrease in the proportion of molecules scattered in the ST channel. The proportion of molecules scattered in the DI channel on the clean surface reduces sharply at incident energies E < 200 meV, and is dependent on the total rather than the normal energy of the incident molecules. At energies E < 270 meV, CO molecules which would otherwise have scattered in the DI channel begin to dissociate. Vibrational excitation is rather less effective in accessing the dissociation barrier than translation. We suggest that the dissociation and ST processes take place during the initial collision, and their probabilities are influenced mainly by the molecular rotational degree of freedom. © 1990.