Hannover 2010 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 18: Cluster I

MO 18.3: Vortrag

Donnerstag, 11. März 2010, 11:00–11:15, F 102

Mass-resolved velocity distributions of supersonic jets from supercritical carbon dioxide — •Wolfgang Christen, Tim Krause, and Klaus Rademann — Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, 12489 Berlin

Supersonic molecular beams continue to constitute a versatile and popular tool in science and technology. For instance, jet expansions from dense gases are routinely used to grow clusters and nanoparticles¹⁻³. Surprisingly, the fundamental aspects of high pressure jet expansions have not been studied in much detail, and little is known on condensation processes close to the critical point. Attempting to improve this situation and advance the comprehension of supersonic jet expansions from supercritical fluids^4,5 we have investigated pulsed, supersonic beams of pure CO₂ at source conditions up to and beyond the critical point (7.38 MPa, 304.13 K). Employing mass-resolved time-of-flight measurements, cluster intensities and terminal flow velocities are reported as a function of stagnation pressure (0.5−11 MPa) and temperature (300−355 K). The experimental results are compared with model predictions of a real fluid treatment of the jet expansion. These calculations⁶ provide a consistent physical picture of the supersonic jet expansion of supercritical fluids and permit valuable insights into the nonequilibrium processes at high supersaturations.

¹ J. Am. Chem. Soc. 108, 2100, 1986. ² Rev. Sci. Instrum. 75, 5048, 2004. ³ J. Phys. Chem. C 112, 17102, 2008. ⁴ J. Chem. Phys. 125, 174307, 2006. ⁵ J. Chem. Phys. 113, 388, 2009. ⁶ Phys. Scr. 80, 048127, 2009.