Abstract
Single-photon photodetachment of mass-selected W −n clusters has been studied by velocity map imaging: Photoelectron imaging allows us to measure simultaneously the kinetic energy spectrum and the angular distribution of photoelectrons, a clear distinction between the isotropic thermionic emission and the anisotropie direct photoemission. A careful study of threshold electrons shows that the thermal distribution p(ε) cannot be described, even qualitatively; by a simple exponentially decreasing Boltzmann function, as is usually assumed. On the contrary, our results are in excellent agreement with more reined iecïretical models. Our results indicate that the transition towards a bulk-like statistical behavior of the internal energy redistribution occurs in very small systems, because of the high density of states in metal clusters. The asymmetry parameter β of the most intense band observed in direct photoemission for each cluster decreases monotonically with size; the direct photoemission of small systems is strongly anisotropie, and becomes isotropic as the size of the system increases. This probably indicates the loss of coherence induced by electron-electron collisions occurring in large systems prior to electron-phonon coupling.
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Pinaré, J.C., Baguenard, B., Bordas, C., Broyer, M. (1999). Angular distributions in photoelectron spectroscopy of small tungsten clusters: competition between direct and thermionic emission. In: Châtelain, A., Bonard, JM. (eds) The European Physical Journal D. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-88188-6_5
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DOI: https://doi.org/10.1007/978-3-642-88188-6_5
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