AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeM

Paper SS3-WeM1
Rainbow Scattering of Methane and Ethane Molecular Beams from a LiF(001) Surface: Dependencies on Incident Kinetic Energy and Molecular Anisotropy

Wednesday, October 4, 2000, 8:20 am, Room 210

Session: Gas/Surface Dynamics
Presenter: T. Kondo, University of Tsukuba, Japan
Authors: T. Kondo, University of Tsukuba, Japan
T. Tomii, University of Tsukuba, Japan
S. Yamamoto, University of Tsukuba, Japan
Correspondent: Click to Email
An experiment to measure the angular distribution of the intensity of the alkane molecular beams scattered from a highly corrugated surface of LiF(001) has been carried out in high resolution, as a step toward the understanding of the fundamental characteristics of surface chemical reactions. One of the two major findings of the experiment shows that the rainbow peaks of the molecular beam was found to depend on its incident kinetic energy. For the clarification of this dependency, we calculated the angular distribution applying the Washboard model@footnote 1@ to fit the results by changing the amplitude of the sinusoidal corrugation in each case of different incident kinetic energy, instead of fixing the amplitude once fitted for the lowest incident kinetic energy. In this way it was further confirmed that the intensity of the rainbow peaks was reduced as the incident kinetic energy increases, contrary to the result predicted with the fixed amplitude. The reason for this discrepancy is thus because the combined structure of Li and F ions weakens the corrugation of the potential energy surface for the beam with increased incident kinetic energy. As the other major finding, the ethane molecular beam shows only one peak but not the rainbow peaks, in spite of negligible difference in the molecular size between the methane and the ethane molecules. On the other hand, the Ar atom which is heavier than both the above alkane molecules shows the distinct rainbow peaks. It is then presumed that the effect of neither the size nor the mass of the molecule is essential for the rainbow peaks. Therefore, the difference in behavior between the methane and the ethane molecules can be understood as a result of the large anisotropy of the ethane molecule. @FootnoteText@ @footnote 1@J. C. Tully. J. Chem. Phys. 92, 680 (1990).