Photoionization at Surfaces: Connections between Photoemission, Hole Decay, and Photodesorption from Adsorbate Layers

Abstract

The time evolution of events connected to photoabsorption in adsorbate layers can be subdivided into primary (photoexcitation/ionization including multiple excitations and screening), secondary (Auger decay in the case of core excitations), and tertiary (bond-breaking) processes. On all these stages, manybody interactions are important. Improved understanding can be gained, if all these processes are viewed together. For adsorbate core excitations on metal surfaces, these connections are examined in some detail, using recent data. Auger spectra for the decay of well-defined primary excitations show that essentially all higher primary excitations have decayed by the time Auger deexcitation occurs; an exception is briefly discussed. On the other hand, the strong influence of delocalization upon the probability of successful bond-breaking leads to an excessive amplification of surviving higher excitations in photodesorption, particularly of fragment ions. To somewhat lesser extent, this is also the case for primary valence excitations and for desorption of neutral and ionic molecules. It is concluded that competition–and possibly even interference–between many-body interactions (screening vs. Coulomb localization) determines this selective branching as seen in electron emission and in desorption.