ELECTRONICALLY INDUCED DYNAMICS IN SURFACE-LAYERS

Electronic excitations induced in well-defined surface layers (adsorba tes as well as condensates) by electron impact or photon absorption ev olve in time in terms of both internal and external coordinates of the electrons as well as of the nuclei. A survey is given to show how the combination of electron spectroscopies with the analysis of desorbing particles (fragments and molecules) liberated by such excitations can be used to investigate the interplay of these evolutions with each ot her. Of particular interest is the coupling of internal modes of the s urface species to the substrate or the surroundings in terms of energy and charge exchange. First the main principles governing these proces ses that have become understood over the years are briefly summarized. On this basis some recent, partly quite unexpected results are discus sed. The first utilizes laser spectroscopy for a detailed analysis of the energy distribution over the internal modes of molecules desorbed by electron impact; the other two combine electron and ion yields unde r highly resolved photon irradiation of condensates. They illustrate t he potential of such investigations for the understanding of the mecha nisms of electronically induced desorption, of the analysis of changes induced in the molecular properties by the situation at the surface o r in the condensate including symmetry breaking in the surface field, and for the improved assignment and selective detection of complex exc itations in solids, surfaces, and molecules.