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Rydberg-like surface states are identified at Au(100) and Cu(100) surfaces by use of inverse photoemission with tunable photon energy. The binding energy (0.6 eV below vacuum) and width ({≤} 0.3 eV full width at half maximum) of the $n=1$ state agree well with previous calculations. Theory yields the expectation that these states represent a widespread phenomenon at surfaces.
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Straub et al. (1984) studied this question.
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