On the Distortion of Scattering Patterns of Molecular Beams from Solid Surfaces

Abstract

In experimental investigations of the gas-solid interactions by a molecular beam, it is desirable to measure the spatial distribution of the reflected molecules from solid surfaces. The effect of finite diameter of the incident beam and geometrical inaccuracies, i.e., discrepancy between the center of rotation of the detector and the point of incidence of the beam on the target, is analyzed theoretically, and the resulting distortions of the scattering patterns are calculated for the limiting case of perfectly diffuse scattering. It has been pointed out that these effects are enhanced when the beam impinges on the target at a glancing angle. For instance, for the incident angle θi=85°, the beam diameter ratio d/ro=0.05 and the displecement ratio or the target surface t/ro=0.02, the maximum intensity of the reflected beam appears at -12° and the apparent error of intensity from the cosine law is about 57 percents.