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DY: Dynamik und Statistische Physik

DY 11: Fluid dynamics I

DY 11.3: Vortrag

Montag, 24. März 2003, 10:30–10:45, G\"OR/229

Molten alkali halides: Model systems for “fast sound”? — •Franz Demmel¹, Shinya Hosokawa², Christoph Hörentrup², Christian Pilgrim², and Maren Lorenzen³ — ¹ILL F-38042 Grenoble — ²Universität Marburg Physikalische Chemie, Marburg — ³ESRF F-38043 Grenoble

Inelastic X-ray scattering has been used to measure the density fluctuations of molten alkali halides. The experiments have been carried out at the inelastic beamline ID28 of the ESRF (Grenoble). With synchrotron radiation we could study the excitations in particular in the low momentum transfer range, where they do not interfere with optic type excitations. The inelastic excitations could be observed and analysed directly from the spectra. The deduced sound velocity for molten NaCl is about 70 % higher than the adiabatic sound velocity. Surprisingly the derived dispersion is very similar to the one of liquid Sodium [1]. This fact can be interpreted, that the particle density fluctuations are mainly driven by the movement of the lighter and smaller subsystem. A recently performed experiment on molten KCl shows the same trend. A quantitative comparison will be given with predictions for the famous fast sound in binary liquids [2].

[1] F. Demmel, S. Hosokawa, M. Lorenzen, W.C. Pilgrim, PRL submitted

[2] J. Bosse, G. Jacucci, M. Ronchetti, W. Schirmacher, PRL 57, 3277 (1986)