SCATTERING OF THERMAL ENERGY GAS BEAMS BY METALLIC SURFACES II

Scattering of molecular gases from platinum and tantalum was studied using an ultra-high vacuum molecular beam apparatus. Beams of the rare gases, nitrogen, oxygen, methane and water vapor were used. The angle of maximum intensity of the scattered gas beams had a dependency on experimental variables that was in fair agreement with theory. Surface contamination and roughness affected the intensity and spatial distribution of scattered beams, but no difference between polycrystalline and single crystal metal surfaces was observed. By using phase-sensitive-detection techniques, the velocity of scattered molecules was found to vary with angular position about the surface. Energy and momentum coefficients were evaluated from the experimental data. Under certain conditions, discontinuities and negative values were found for these coefficients; such excursions in energy accommodation have been theoretically predicted. The experimental results were used in analysis of free molecule and slip flows. (Author)