Hannover 2010 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 18: Cluster I
MO 18.4: Vortrag
Donnerstag, 11. März 2010, 11:15–11:30, F 102
Understanding the velocity bifurcation in supersonic jet expansions — •Wolfgang Christen1, Klaus Rademann1, and Uzi Even2 — 1Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, 12489 Berlin, Germany — 2Sackler School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel
The comprehension of homogenous nucleation processes is of fundamental relevance for many research fields, including atmospheric chemistry and materials science. Supersonic beams provide the possibility to address this topic under very well defined experimental conditions, even at very high degrees of supersaturation.
At higher densities of the working fluid, the velocity distribution of the generated jet is severely affected by cluster formation, eventually giving rise to several peaks1−6. So far, however, these observations were phenomenological in nature, with no quantitative explanation possible.
Attempting to improve this situation and advance the comprehension of supersonic jet expansions at high source densities we have studied the transition to a second peak in the velocity distributions of free-jet expansions from supercritical fluids using mass-resolved time-of-flight measurements. These experiments are complemented by a thermodynamic description of the isentropic expansion process, considering the initial and final fluid enthalpies. For the first time this model permits a quantitative prediction of the velocity bifurcation.
1 J. Chem. Phys. 92, 6875, 1990.
2 Phys. Rev. Lett. 64, 1899, 1990.
3 J. Chem. Phys. 102, 6258, 1995.
4 ibidem 106, 3348, 1997.
5 ibidem 125, 174307, 2006.
6 J. Phys. Chem. A 113, 388, 2009.