The adsorption dynamics of molecular carbon dioxide on Pt(111) and Pd(111)

The dynamics of the nondissociative adsorption of carbon dioxide on Pt(1 1 1) and Pd(1 1 1) were investigated by supersonic molecular beam techniques at a surface temperature of 80 and 60 K. well below the desorption temperatures of 95 and 88 K, respectively. The initial trapping probability of CO, on both Pt(1 1 1) and Pd(1 1 1) scale with normal and near-normal energy scaling functions, indicating smooth gas-surface potentials, On the other hand, trapping on the carbon dioxide-saturated Pt(1 1 1) exhibits a more corrugated gas-surface potential. on which trapping scales as E-T cos(0.7) theta. The probability of carbon dioxide trapping increases with self-coverage and is Successfully described by the modified Kisliuk model. indicating that trapping into the extrinsic precursor state is more efficient than trapping on the clean surface. The coverage of carbon dioxide into Pt(1 1 1) saturates at about 0.275 ML at a surface temperature of 80 K as a result of beam exposure at normal incidence at 8.5 kJ/mol. The stochastic. three-dimensional classical dynamics for the simulation of CO, on Pt(11 1) indicates that the excitation of surface phonons on the first bounce determines trapping on Pt(1 1 1). The same set of Morse potentials were employed to predict the CO, trapping on Pd(1 1 1). In general. the prediction agrees reasonably with the experimental results. The difference between the calculated trapping probabilities from simulations and the experimental values is within 20%. (C) 2001 Published by Elsevier Science B.V.