On the concept and distribution of reactive sites in dissociative chemisorption

Abstract

We present results of classical stochastic molecular dynamics simulations of dissociative chemisorption in two different model systems, H2 /Ni(100) and N2 /W(110). Based upon the separation of time scales between dissociation and translations and rotations, we determine: (1) the location of the dissociation within the unit cell of the surface and (2) the orientation of the molecule at the time of dissociation. The two systems displayed opposite and unusual behavior with the former exhibiting site selectivity even though S0 ≊0.8 and the latter exhibiting nonsite selectivity for S0 ≊0.13. This behavior is explained in terms of the characteristics of the molecule–surface and atom–surface interaction potentials and the general strength of adsorbate-surface vs surface–surface bonds.