Quantum-resolved stimulated desorption and dissociation processes of adsorbed molecules

The electronic excitations and subsequent dynamics responsible for the stimulated desorption and dissociation of adsorbed molecules on metal surfaces can be characterized in detail by examining the neutral gas-phase products in a quantum specific fashion. Specifically, we have studied the electron-stimulated desorption (ESD) of NO from clean and O-covered Pt(111), and the electron-stimulated dissociation of NO₂ on clean Pt(111) through state-selective, time-of-flight laser resonance-ionization of the NO product. In these experiments, we can determine the nature of a given electronic excitation by determining the threshold for the stimulated process and correlating it with photoelectron spectra and calculated excitation lifetimes. By determining the translational, vibrational, and rotational energy distributions of the ESD or stimulated dissociation products, a dynamical picture emerges which can be directly correlated with the electronic excitation and the extent of charge-transfer screening from the substrate. The presence of co-adsorbates such as atomic O modify screening charge and thus directly affect both the lifetimes of excitations and the dynamics of the stimulated event.