Quantum and mixed quantum/classical calculations of the photolysis of a HCl adsorbate on a MgO surface are reported. In the quantum calculation of the hydrogen dynamics ͑with rigid surface and chlorine atoms͒ a strong oscillatory structure is found in the angular distribution of the photofragmented hydrogen as well as in the absorption spectrum. These resonances are caused by temporary trapping of the hydrogen atom between the chlorine atom and the surface and reflect the initial perpendicular adsorption geometry. Corrugation of the surface potential leads to a significant modification of these interference patterns, which exist even for a flat surface. Within a mixed quantum/classical time-dependent self-consistent field ͑Q/C TDSCF͒ propagation the influence of surface degrees of freedom on the interference patterns is investigated. The thermal motion of the surface and inelastic collisions of the hydrogen atom with the surface and the chlorine atom washes out most of the oscillatory structure. In the fully angular and energy resolved spectra nevertheless clearly distinguishable peaks are seen. They can be used in practice to extract information about adsorption geometry and surface potential parameters.
The photodissociation of HCl/MgO ͑001͒ is studied by classical molecular dynamics of a single adsorbate system including the substrate phonon modes. An important quantum effect is accounted for by taking the hydrogen coordinates and momenta in the initial state from a vibrational ground state wave function. In the angular distribution of the scattered photofragments characteristic structures due to rainbows, scattering shadow and resonances are found, that are already well described within the rigid surface approximation. The hydrogen kinetic energy release also shows a pronounced peak structure corresponding to different energy transfer mechanisms and is significantly affected by inclusion of energy transfer to the phonon modes. Due to multiple collisions with the surface and the chlorine, the hydrogen can lose more than 3.5 eV of its 4.7 eV excess energy. The angular resolved energy spectrum is explained by several types of trajectories connected with the above mechanisms. The results suggest further that the different mechanisms can be separated in an experiment.
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