ADSORPTION OF HYDROGEN ON TUNGSTEN - A PRECURSOR PATH PLUS DIRECT ADSORPTION

Using nozzle beams we have determined the adsorption dynamics of H-2/W. On the rough (111) and (100) surfaces hydrogen adsorbs at low particle energies almost exclusively through a precursor path; at high beam energies a direct, activated path is used. For the low energy precursor path a dependence on surface temperature is observed. Hydrogen adsorption on the W(110) surface proceeds via a direct activated path. The direct adsorption path for all crystals exhibits a forward directed distribution for the sticking coefficient; in contrast at low particle energies the precursor path shows a minimum of the sticking coefficient in the direction of the surface normal.