We report experimental energy distributions and yields of electrons emitted from MgO surfaces under the impact of slow noble gas and sodium singly charged ions at varying incident energies. At impact energies below similar to 1 keV, electron spectra are nearly independent of ion type and energy. A tail of high-energy electrons is observed to grow at higher impact energies. The results are explained in terms of promotion of oxygen-2p electrons during binary projectile-oxygen collisions populating continuum and excitonic states. Excitons can significantly contribute to electron emission due to the negative electron affinity of the surface. (c) 2005 Elsevier B.V. All rights reserved.
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