Transition of the electronic response from molecular-like to jellium-like in cold,small sodium clusters |
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Authors: | Christoph Ellert Martin Schmidt Thomas Reiners Hellmut Haberland |
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Institution: | 1. Fakult?t für Physik, Universit?t Freiburg, H.Herderstasse 3, Freiburg, D-79104, Germany
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Abstract: | Absolute photoabsorption cross sections for Na n + (2≤n≤21) were measured in the visible energy range. The cluster ions were produced in a gas aggregation source and thus have a canonical distribution of internal energy corresponding to a temperature of ~ 105 K. The spectra for n≤9 and 11 exhibit between two and six absorption lines, and are in qualitative agreement with ab inito quantum chemical calculations. For n=15 and 21, the position of the resonances can be explained as excitations of a nearly free electron gas in a spheroidal container. An evolution is thus observed from molecular-like transitions to a giant collective resonance of the electron cloud. The integrated oscillator strength is 0.95 per 3s-electron in the energy range covered for n≥4, showing that the main excitations of the valence electrons have been found. |
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