Hamburg 2009 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 14: Cluster

MO 14.5: Vortrag

Mittwoch, 4. März 2009, 15:15–15:30, VMP 6 HS-F

Observing Phase Transitions in Supersonic Molecular Beams — •Wolfgang Christen and Klaus Rademann — Institut für Chemie, Humboldt-Universität zu Berlin, 12489 Berlin

One question of current interest is the maximum cooling and slowing that can be achieved in supersonic beam expansions [1]. While pulsed jets from compressed gases are successfully used to transfer nonvolatile and thermally labile molecules into the gas phase [2,3], the influence of thermodynamic properties (pressure, temperature, aggregation state) on beam velocity and beam temperature remains unclear to a large extent.

We therefore address the question, both theoretically and experimentally, if phase transitions of a substance can be probed using high-resolution time-of-flight analysis of supersonic beam expansions. We compare the validity of different formulas describing supersonic beam characteristics and present experimental results for a wide range of stagnation pressures and stagnation temperatures, including the gas-liquid, gas-supercritical, and liquid-supercritical phase transitions of ethylene and propane.
[1] Wolfgang Christen and Klaus Rademann, Phys. Rev. A 77(1), 012702 (2008).

[2] Wolfgang Christen, Stephanie Geggier, Svitlana Grigorenko, and Klaus Rademann, Rev. Sci. Instrum. 75(11), 5048-5049 (2004).

[3] Wolfgang Christen, Tim Krause, and Klaus Rademann, Int. J. Mass Spectrom. 277(1-3), 305-308 (2008).