Studies of Molecular Scattering at the Solid Surface

Abstract

Experimental studies of molecular scattering at the gas‐surface interface are described in which molecular beams of N₂ were scattered at surfaces of steel, aluminum, and glass. Polar surveys of the issuing molecule flux indicate the scattering to be well represented by a cosine distribution in most cases. A moderate deviation from such a distribution was observed in the case of the glass‐N₂ interaction. It is shown how measurements of scattering at the surface may be used to derive values of the momentum transfer coefficient, f(s), in a rarefied gas flow where s is defined as the ratio of the mass speed of the flow to the most probable thermal speed of the molecules. In order to complete the calculation where scattering information alone is available from experiment, assumptions must be made relating to the energy exchange at the surface. In the case of the present calculation, where a surface interaction model was formed in part from the glass ‐N₂ scattering data, two extremal assumptions relating to the energy exchange lead to values of f(s) of approximately 0.97 at s=0.1.