Quantum dynamics of the dissociation of H-2 on Cu(100): Dependence of the site-reactivity on initial rovibrational state

We perform six-dimensional (6D) quantum wavepacket calculations for H-2 dis sociatively adsorbing on Cu(100) from a variety of rovibrational initial st ates. The calculations are performed on a new potential energy surface (PES ), the construction of which is also detailed. Reaction probabilities are i n good agreement with experimental findings. Using a new flux analysis meth od, we calculate the reaction probability density as a function of surface site and collision energy, for a variety of initial states. This approach i s used to study the effects of rotation and vibration on reaction at specif ic surface sites. The results are explained in terms of characteristics of the PES and intrinsically dynamic effects. An important observation is that , even at low collision energies, reaction does not necessarily proceed pre dominantly in the region of the minimum potential barrier, but can occur al most exclusively at a site with a higher barrier. This suggests that experi mental control of initial conditions could be used to selectively induce re action at particular surface sites. Our predictions for site-reactivity cou ld be tested using contemporary experimental methods: The calculations pred ict that, for reacting molecules, there will be a dependence of the quadrup ole alignment of j on the incident vibrational state, v. This is a direct r esult of PES topography in the vicinity of the preferred reaction sites of v=0 and v=1 molecules. Invoking detailed balance, evidence for this differe nce in preferred reaction site of v=0 and 1 molecules could be obtained thr ough associative desorption experiments.