Quantum dynamics of reactive scattering of H2 from metal surfaces.

G.J. Kroes, Leiden Institute of Chemistry, Leiden University.

The dissociative chemisorption of H2 on metal surfaces is a benchmark system 
for molecule-surface reactions relevant to heterogeneous catalysis. Comparison 
of theory to experiment allows us to assess how well heterogeneously catalysed 
reactions can be described from first principles.
Computational results will be presented on the scattering of H2 from 
Cu(100), Cu(111), Pd(111), and Pt(111). The calculations are based on 
potential energy surfaces (PESs) computed with density functional theory (DFT) 
or based on DFT. These are used in time-dependent wave packet calculations 
treating all six molecular degrees of freedom of H2  quantum mechanically. 
Quantum dynamics calculations on both H2 + Cu(100) and Pt(111) show that 
accurate reaction probabilities may be obtained using an accurately fitted 
DFT-GGA PES, if all six hydrogen molecular degrees of freedom are treated. The 
dependence of the reaction probability on incidence angle is also well 
described. Furthermore, in many cases the calculations allow useful 
interpretations of previous experiments. In a recent example, we were able to 
solve a paradox regarding the corrugation of a Pt(111) surface as seen by H2 
in reaction and in scattering. 
The application of the method to molecular diffraction will also be discussed. 
As will be shown for H2 + Pd(111), molecular diffraction, which is typically 
viewed as a quantum phenomenon, can be remarkably well described by classical 
mechanics. Quantum dynamics based on accurately fitted DFT potentials yield 
diffraction intensities in very good agreement with experiment for 
H2 + Pd(111), and theory and experiment for this systems show that out-of-plane 
diffraction can be much more important than in-plane diffraction for H2 + metal 
surface systems.
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