CO2 sticking on Pt(111); the role of kinetic energy and internal degrees of freedom.

by D. Kulginov, M. Persson, C. Åkerlund, I. Zoriç, and B. Kasemo, J. Vac. Sci. Techn. A13, 1511 (1995)

Abstract

CO2 adsorbed on Pt(111) is a system that have several attractive features that makes it suitable for studies of the role of internal degrees of freedom on the sticking process. In particular, this relatively long and linear molecule has a low energy vibrational mode. We have carried out measurements of non-dissociative sticking coefficient, S0, of CO2on the Pt(111) surface in the zero coverage limit as a function of incident kinetic energy, Ei, at different angles of incidence. A most interesting feature of the measured S0 for this physisorption system is its slow decline from 0.6 at Ei=60 meV towards a value of S0 \approx 0.1 at the highest measured energy of 1.2 eV. Our classical trajectory studies suggest that the observed high energy tail of S0 is primarily due to translational-rotational (T-R) energy transfer in the initial collision of the molecule with the surface while the effects of the intramolecular vibrations on S0 are negligible. The calculated S0 depends non-monotonically on the rotational anisotropy of the molecule--surface interaction. This is shown to be an effect of the dramatic influence of the number of bounces made by the two ends of the molecule against the surface in the initial collision on the T-R energy transfer.