Analysis of H2 dissociation dynamics on the Pd(111) surface

CRESPOS, C.; BUSNENGO, H.F.; DONG, W.; SALIN, A.

JOURNAL OF CHEMICAL PHYSICS

Año: 2001 vol. 114 p. 10954 - 10962

0021-9606

We perform a detailed analysis of the dynamics of the dissociative adsorption of H2 molecules on a Pd(111) surface using ab initio data for the molecule–surface interaction and classical trajectorymethods. We show that the reaction probability is completely determined by the molecule–surface interaction in the approach toward the surface before it reaches a critical distance of 1.5 Å. Thecorresponding dynamics can be reduced to a 2D one, involving only the translational and rotational degrees of freedom, except in the lower energy range where an important role is played by dynamictrapping. We establish the relation between the dissociation probability and the shape of 2D cuts of the potential energy surface using a simple model of the evolution of orientational forces as the molecule approaches the surface. Whereas above 1.5 Å the molecule evolves "as a whole", below 1.5 Å the dynamics has the character of independent atom–surface interactions which explains why it dissociates with a probability close to one once it has reached the critical distance of 1.5 Å.