Accommodation coefficient of tangential momentum on atomically clean and contaminated surfaces

Experimental data on the accommodation coefficient of the noble gases on various surfaces are presented. The accommodation coefficient is measured via the mass flow rate of the gas through a capillary in the free-molecular regime. Three types of the surface are studied: atomically clean silver, atomically clean titanium and titanium coated by oxygen. It is shown that for the atomically clean surfaces the accommodation coefficient depends significantly on the species of the gas. For the surface coated by oxygen the accommodation coefficient is close to unity.