We report rapid deterioration of metallic surfaces on irradiation with ultraviolet light. Very fast degradation of the Shockley state of Cu(111) is observed during photoemission at low temperature. A different evolution of the Shockley states during annealing and cooling was also discovered. These observations seem to favor a mechanism based on photon-stimulated chemisorption of hydrogen on the surface. We suggest that this mechanism affects all experiments involving intense radiation and might become a major obstruction for future experiments with microfocused beams.
