Electron–hole pairs during the adsorption dynamics of O₂on Pd(100): exciting or not?

During the exothermic adsorption of molecules at solid surfaces dissipation the released energy occurs via the excitation of electronic and phononic of freedom. For metallic substrates the role of the nonadiabatic excitation channel has been controversially discussed, as the of a band gap could favour an easy coupling to a manifold of pairs of arbitrarily low energies. We analyse this situation for highly exothermic showcase system of molecular oxygen dissociating at(100), using time-dependent perturbation theory applied to first-principles-structure calculations. For a range of different trajectories of O2 molecules we compute largely varying electron-hole pair spectra, underlines the necessity to consider the high-dimensionality of the dynamical process when assessing the total energy loss into this channel. Despite the high Pd density of states at the Fermi level, concomitant non-adiabatic energy losses nevertheless never exceed about 5% the available chemisorption energy. While this supports an electronically description of the predominant heat dissipation into the phononic, we critically discuss the non-adiabatic excitations in the context of O2 spin transition during the dissociation process.