Improvements in the description of the surface spin relaxation of atomic hydrogen

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Abstract
Some possibilities are explored to explain the large discrepancy between theoretical and experimental spin-relaxation rates for the lowest two hyperfine states of hydrogen atoms adsorbed at a helium surface. A three-dimensional description of the collision process of adsorbed atoms is presented, including the coupling of the motions parallel and perpendicular to the surface by the triplet potential. Also the possibility of surface dimers, i.e., triplet bound states at the surface, is studied. Deviations from the high-temperature limit, used in previous papers, are investigated. Effective-mass and surface-deformation effects, resulting from the participation of helium-film modes in the H-H collision process are studied. It turns out that none of the model improvements considered decreases the discrepancy with experiment significantly, except possibly for the surface-deformation effect.