Momentum-resolved inverse photoemission

Inverse photoemission including isochromat spectroscopy is shown to be a versatile technique to probe empty electronic states in solids and at clean and adsorbate covered surfaces. The complete set of quantum numbers of an electronic state can be determined and examples will be discussed for bulk and surface electronic states. For sufficiently low kinetic energy of the primary electrons, inverse photoemission is shown to be applicable to adsorbates also. This allows one to assess directly the unoccupied electronic states of the adsorbate which play an important role in the formation of the surface chemical bond. Examples are discussed for atomic and molecular chemisorption as well as adsorption on alkali promoted surfaces.