Time of flight spectra in thermal desorption of helium |
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Authors: | ZW Gortel HJ Kreuzer M Schäff G Wedler |
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Institution: | Department of Physics, Dalhousie University, Halifax, Nova Scotia, B3H 3J5 Canada;Institut für Physikalische und Theoretische Chemie, Universität Erlangen — Nürnberg, Egerlandstrasse 3, D-8520 Erlangen, Fed. Rep. of Germany |
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Abstract: | Time of flight spectra are calculated within the cascade model of phonon-mediated desorption for helium desorbing from graphite, sapphire and Nichrome. One and three-dimensional theories are compared. Deviations from Knudsen's cosine law are traced to dynamical effects. The spectra are — as a function of time — narrower than a Maxwellian distribution and their maxima are generally shifted to shorter times indicating that the desorbed molecules are hotter than the solid temperature. Relevant experiments are discussed. Experimental geometries are analysed. |
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