Theoretical Investigations of Gas–Solid Interaction Phenomena. III. Adsorbed Particles and Lattice Impurities

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Abstract
A study of the interaction of gaseous particles with contaminated surfaces is reported. An extension of the three‐dimensional classical model previously used by the authors to study gas–solid interactions at clean surfaces is employed. The surface is assumed to consist of nine movable lattice atoms and one or two movable adsorbed particles. Morse potential functions are assumed to exist between the incident gaseous atom and each of the movable surface atoms while Lennard‐Jones (12–6) potentials operate between the adparticles and the lattice. Numerical solution of the Hamiltonian equations that describe He interacting with Ar absorbed on a Ni lattice (He/Ar/Ni) yields energy‐transfer coefficients and spatial distributions of reflected atoms. The energy‐transfer coefficient (ETC) is found to reach a maximum at a half‐monolayer of adatom coverage due to changes in surface roughness. The ETC is also found to increase with decreasing adatom mass and adatom–lattice binding energy. It is a strong but irregular function of the surface particle vibration phases. The spatial distributions show a maximum amount of backscatter and out‐of‐plane intensity for half‐monolayer coverage. A study of He scattered from an Ni surface containing oxygen impurity atoms indicates that quasispecular scattering is possible in such cases. The results of the model are qualitative due to an inadequate number of surface atoms, a lack of knowledge about the nature of the surfaces, and uncertain interaction potential parameters.