Numerically stable solution of coupled channel equations: The local reflection matrix

Dynamical Quantum Filtering via Enhanced Scattering of para-H2 on the Orientationally Anisotropic Potential of SrTiO3(001)

Quantum dynamics calculation, performed on top of density functional theory (DFT)-based total energy calculations, show dynamical quantum filtering via enhanced scattering of para-H2 on SrTiO3(001). We attribute this to the strongly orientation-dependent (electrostatic) interaction potential between the H2 (induced) quadrupole moment and the surface electric field gradient of ionic SrTiO3(001). These results suggest that ionic surfaces could function as a scattering/filtering media to realize rotationally state-resolved H2. This could find significant applications not only in H2 storage and transport, but also in realizing materials with pre-determined characteristic properties.

Extraordinarily large kinetic isotope effect on alkene hydrogenation over Rh-based intermetallic compounds

A series of Rh-based intermetallic compounds supported on silica was prepared and tested in alkene hydrogenation at room temperature. H₂ and D₂ were used as the hydrogen sources and the kinetic isotope effect (KIE) in hydrogenation was studied. In styrene hydrogenation, the KIE values differed strongly depending on the intermetallic phase, and some intermetallic compounds with Sb and Pb exhibited remarkably high KIE values (>28). An extraordinarily high KIE value of 91, which has never been reported in catalytic reactions at room temperature, was observed particularly for RhPb₂/SiO₂. RhPb₂/SiO₂ also showed high KIE values in the hydrogenation of other unsaturated hydrocarbons such as phenylacetylene and cyclohexene. The density functional theory calculation focused on the surface diffusion of hydrogen suggested no contribution of the quantum tunneling effect to the high KIE values observed. A kinetic study revealed that the dissociative adsorption of H₂ (D₂) was the rate-determining step in the styrene hydrogenation over RhPb₂/SiO₂. We propose that the large KIE originates from the quantum tunneling occurring at the hydrogen adsorption process with the aid of the specific surface structure of the intermetallic compound and adsorbate alkene.

High-dimensional quantum dynamical study of the dissociation of H2 on Pd(110)

We report the first six-dimensional quantum dynamical study of the dissociative adsorption of H(2) on a (110) surface. We have performed quantum coupled-channel calculations for the system H(2)/Pd(110) based on a potential energy surface (PES) that was derived from ab initio electronic structure calculations. In particular, we have focused on the effects of the corrugation and anisotropy of the PES on the H(2) dissociation probability. Our results agree well with the available experimental data for the sticking probability as a function of the initial kinetic energy and the angle of incidence. Because of the coupling between the anisotropy and corrugation of the potential energy surface our calculations predict an unusual rotational heating and a rather small rotational alignment in desorption.

Multiphonon resonances in the Debye-Waller factor of atom surface scattering

He atom surface scattering by dispersionless phonons is treated employing coupled channel (CC) calculations. At low energies, they predict a behavior opposite to perturbative Born or "exponentiated" Born approximation: strong resonant phonon stimulated elastic and inhibited inelastic scattering. The corresponding resonances have not been observed in earlier CC results since these have considered only the temperature dependence of the Debye-Waller factor at higher energy or omitted the attractive well. The resonances can be interpreted in terms of bound states in the attractive well with several excited vibrational quanta. They may be observable for, e.g., He scattering by a cold Xe/Cu surface.

Molecular beam investigation of hydrogen dissociation on Si(001) and Si(111) surfaces

The influence of molecular vibrations on the reaction dynamics of H2 on Si(001) as well as isotopic effects have been investigated by means of optical second-harmonic generation and molecular beam techniques. Enhanced dissociation of vibrationally excited H2 on Si(001)2 x 1 has been found corresponding to a reduction of the mean adsorption barrier to 390 meV and 180 meV for nu=1 and nu=2, respectively. The adsorption dynamics of the isotopes H2 and D2 show only small differences in the accessible range of beam energies between 50 meV and 350 meV. They are traced back to different degrees of vibrational excitation and do not point to an important influence of quantum tunneling in crossing the adsorption barrier. The sticking probability of H2 on the 7 x 7-reconstructed Si(111) surface was found to be activated both by H2 kinetic energy and surface temperature in a qualitatively similar fashion as H2/Si(001)2 x 1. Quantitatively, the overall sticking probabilities of H2 on the Si(111) surface are about one order of magnitude lower than on Si(001), the influence of surface temperature is generally stronger.

Quantum theory of dissociative chemisorption on metal surfaces

Recent theoretical progress in gas-surface reaction dynamics, a field relevant to heterogeneous catalysis, is described. One of the most fundamental reactions, the dissociative chemisorption of H2 on metal surfaces, can now be treated accurately using quantum mechanics. Density functional theory is used to compute the molecule-surface interaction, and the motion of the hydrogen atoms is simulated using quantum dynamics, modeling all six molecular degrees of freedom. Theory is in good quantitative agreement with molecular beam experiments, offering useful interpretations, and allowing reliable predictions. The success of the approach calls for extensions to larger systems, such as dissociative chemisorption of polyatomic molecules.