The scattering of thermal energy beams of4He, H2, and D2from the (111) surfaces of epitaxially grown Ni and Ag single crystals has been measured. Also measured were the angular dependences of the desorption of HD resulting from the dissociationndash;recombination exchange reaction of H2and D2on active (111) Ni surfaces. The angular desorption dependence of HD is contrary to the Knudsen law and is describable analytically bycosdthgr;rwhere2.5thinsp;thinsp;dthinsp;thinsp;4.0depending on the condition of the particular surface under study. Comparison of these results with the complementary nonreacted scattering distributions, i.e., direct reflection on (111) Ni, indicates that the two measured components, reflection and desorption, combine to yield the total scattered flux from the surface. An artificial synthesis of the total flux distribution expected from the surface assuming an isotropic hydrogen source and the measured reflection and desorption distributions yields a cosine dependence, as expected, at equilibrium. The reflection distributions for the other systems studied are also consistent with this result if a desorption distribution per unit surface area of the formcosdthgr;ris assumed. The results further indicate that adsorption proceeds ascosathgr;inodot;whereathinsp;ap;thinsp;dthinsp;minus;thinsp;1.
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