Interaction between D 2 and N 2 on (100) oriented W foil

Abstract

The coadsorption of D 2 and N 2 on W foil (highly (100) oriented) at 140 K has been studied using temperature programmed desorption (TPD). The chemisorption and desorption of D 2 and N 2 is in agreement with data on W(100). For dosed mixtures of D 2 and N 2, the dissociative adsorption is competitive. Preadsorbed N(a) (or D(a)) blocks the dissociative adsorption of D 2 (or N 2) linearly. The displacement of one adsorbate gas by the other does not occur at 140 K. Coadsorbed N(a) shifts D(a) to a lower energy binding state. On N/W, there is a weakly adsorbed molecular state of D 2 with E d = 5.5 kcal/ mol and v (1) = 10 7.3 s -1. There is an isotope effect for dissociative adsorption of molecular hydrogen on N/W. Evidence that adsorbed molecular N 2 undergoes both desorption and dissociation as the surface temperature increases is given. No direct bonding interaction between N(a) and D(a) is observed. These results demonstrate that the surfaces of W foils annealed to 2900 K are very good approximations to single crystal W(100) surfaces.