Quantum dynamics studies of adsorption and desorption of hydrogen at a Cu(111) surface

Efficient Vibrational Energy Redistribution between Stretching Modes: State-to-State Quantum Scattering of H_{2}O from Cu(111)

State-to-state scattering dynamics of H_{2}O from Cu(111) has been studied by a fully coupled quantum mechanical model which explicitly accounts for the most important molecular degrees of freedom, based on a first-principles determined potential energy surface. When H_{2}O in its antisymmetric O-H stretching vibration (ν_{3}) collides with the surface, we find that the intramolecular vibrational energy redistribution (IVR) is predominant from ν_{3} to the symmetric stretching mode (ν_{1}), while rather inefficient to the bending mode (ν_{2}). This mode-specific IVR results from the strong couplings between stretching modes, which equally dispose the initial energy in ν_{3} into local stretching modes differing by a phase factor. Given the number of stretching modes in H_{2}O and CH_{4}, this mechanism naturally explains why the product ν_{1}/ν_{3} ratio calculated here is ∼3 times over that recently measured for CH_{4} scattering on Ni(111), suggesting that the nonstatistical IVR is more general than expected in polyatomic molecules.

SIX-DIMENSIONAL DYNAMICS OF DISSOCIATIVE CHEMISORPTION OF H2 ON METAL SURFACES

The theory of time-dependent quantum dynamics of dissociative chemisorption of hydrogen on metal surfaces is reviewed, in the framework of electronically adiabatic scattering from static surfaces. Four implementations of the time-dependent wave packet (TDWP) method are discussed. In the direct product pseudo-spectral and the spherical harmonics pseudo-spectral methods, no use is made of the symmetry associated with the surface unit cell. This symmetry is exploited by the symmetry adapted wave packet and the symmetry adapted pseudo-spectral (SAPS) method, which are efficient for scattering at normal incidence. The SAPS method can be employed for potential energy surfaces of general form.

Comparison to experiment shows that the TDWP method yields good, but not yet excellent, quantitative accuracy for dissociation of (ν = 0, j = 0) H 2 if the calculations are based on accurately fitted density functional theory calculations that are performed using the generalized gradient approximation. The influence of the molecule's vibration (rotation) is well (reasonably well) described. The theory does not yet yield quantitatively accurate results for rovibrationally inelastic scattering. The theory has helped with the interpretation of existing experimental results, for instance, by solving a parodox regarding the corrugation of Pt(111) as seen by reacting and scattering H 2. The theory has also provided some exciting new predictions, for instance, concerning where on the surface of Cu(100) H2 reacts depending on its vibrational state. Future theoretical studies of H 2 reacting on metal surfaces will likely be aimed at validating GGAs for molecule-surface interactions, and understanding trends in collisions of H 2 with complex metal surfaces.