Abstract
Adsorbate ionization energies (energy levels) have been calculated for a number of metal-adsorbate systems that have been studied recently by ultraviolet photoelectron spectroscopy. The method, which is only applicable to highly "ionic" metal-adsorbate systems, is based on a point-charge-cluster approximation to the metal-adsorbate system. Values of the adsorbate ionization energies calculated by this method agree with experiment within at least 10% for the metal-adsorbate systems investigated.