Phononic dissipation during "hot" adatom motion: A QM/Me study of O dissociation at Pd surfaces.

We augment ab initio molecular dynamics simulations with a quantitative account of phononic dissipation to study the non-equilibrium aftermath of the exothermic oxygen dissociation at low-index (111), (100), and (110) Pd surfaces. Comparing the hyperthermal diffusion arising from a non-instantaneous dissipation of the released chemical energy, we find a striking difference in the resulting "hot" adatom lifetime that is not overall reflected in experimentally recorded product end distances. We rationalize this finding through a detailed mode-specific phonon analysis and identify the dominant dissipation channels as qualitatively different groups of localized surface modes that ultimately lead to intrinsically different rates of dissipation to the Pd bulk. The thus obtained first-principles perspective on non-equilibrium adsorbate-phonon dynamics thereby underscores the sensitive dependence on details of the phononic fine structure, while questioning prevalent assumptions about energy sinks made in commonly used model bath Hamiltonians.