ANOMALOUS 5P PHOTOEMISSION OF XENON ADSORBED ON PD(110)

The UPS derived 5p 3 2, 1 2 ionization potentials of xenon adsorbed on a Pd(110) surface are found to increase by 0.36 eV as the relative xenon coverage increases from zero to monolayer saturation. This coverage dependent shift of adsorbate peaks on a metal substrate appears to be a fundamental novelty. Possible mechanisms which may lead to such a peak shift are discussed. Furthermore a selectively enhanced width of the Xe 5p 3 2 peak and a slightly reduced spin-orbit splitting for adsorbed xenon as compared to gaseous xenon are detected. Both observations are incompatible with a final state image field interpretation but might tentatively be ascribed to initial state image field interactions. © 1979.