Interactions between Chemisorbed Species: H2 and N2 on (100) Tungsten

The interactions between hydrogen and nitrogen adsorbed species on a (100) tungsten crystal have been investigated by flash desorption methods. When the crystal covered with a monolayer of hydrogen is exposed to gaseous N2, the nitrogen slowly replaces the two chemisorbed hydrogen β states by means of a slight lowering of the hydrogen desorption energy. This displacement process occurs via slow thermal desorption of hydrogen in the presence of gaseous N2 when the surface temperature is ≳300 K no such replacement is observed at 273 K. Coverage measurements indicate that there is a stoichiometric ratio between N atoms adsorbed and H atoms displaced from the crystal at ∼300 K. Although virtually no hydrogen will adsorb on the nitrogen-covered surface at 300 K, several weakly bound hydrogen states are populated at 100 K on this surface. No chemical difference between the β1 and β2 hydrogen species was detected, suggesting that both states originate from adsorbed atoms.