Messung der Verweilzeit von He-Atomen an Glasoberflächen

Abstract

Mean sticking times of helium on a glass surface are determined at very low pressures from nonstationary molecular flow through glass capillaries. The temperature range covered is 13.8 °K to 20.4 °K.

Resulting sticking times are of the order of 10⁻⁷ to 10⁻⁵ sec. They show a characteristic dependence on temperature and pressure.

These measurements can be interpreted by means of a simple model: He-atoms mostly are bound to the surface with an adsorption energyE of 229 cal/mol≙0.01 eV (±20%). However with a probability of 10⁻⁴ the energy is 530 cal/mol≙0.023 eV (±6%). In both cases sticking times τ follow the equation τ=τ₀exp(E/RT) where τ₀ is about 10⁻⁹ to 10⁻¹⁰ sec.