SCATTERING OF HYDROGEN-ATOMS FROM LIQUID-HELIUM SURFACES

We analyze in detail experiments in which we study the interaction of atomic hydrogen with liquid-helium surfaces. A theoretical background and a description of the experimental setup is given. A first experiment measured the transmission of hydrogen atoms through a capillary in the temperature interval of 145 < T < 526 mK for He-4 surfaces and 73 < T < 174 mK for He-3 surfaces. To extract the thermally averaged sticking probability s we need a model relating the atomic sticking coefficient s(v) to the capillary transmission K. We analyze our data with a model based on a fixed s(v), resulting in s = 0.33(3)T, and a model based on a speed-dependent s(v), resulting in s = 0.65(6)T. The data show s to be linearly dependent on temperature. We do not observe any significant difference in s between He-4 and He-3 surfaces. In a second experiment we used a hemispherical liquid-helium covered quartz mirror to focus a hydrogen atom beam. The resolution of our setup is about 10 mrad, which is sufficient to study direct near-elastic scattering, providing precision data for the sticking coefficient is available.