Spatial and speed distributions of H2 and D2 desorbed from a polycrystalline nickel surface

The desorption of hydrogen (H₂ and D₂) from a polycrystalline nickel surface has been investigated by measuring the spatial and speed distributions of the desorbed molecules. The Ni specimen was constructed as a membrane with one side exposed to hydrogen at ~ 1 atm pressure and the other side exposed to vacuum, thereby enabling us to supply hydrogen to the test surface via permeation of atoms through the membrane. These atoms recombine on the surface to form molecules that desorb into the evacuated chamber. The spatial distribution of the desorbed molecules was measured with a rotatable ionization gauge, whereas the speed distribution of molecules desorbed along the surface normal was determined by means of a time-of-flight detector in a second apparatus.