Düsseldorf 2007 – scientific programme
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MO: Fachverband Molekülphysik
MO 22: Cold Molecules I (gemeinsam mit Q)
MO 22.7: Talk
Tuesday, March 20, 2007, 12:15–12:30, 6B
Efficient Cooling in Supersonic Jet Expansions of Supercritical Fluids — •Wolfgang Christen1, Klaus Rademann1, and Uzi Even2 — 1Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany — 2Sackler School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel
Pulsed, supersonic beams of carbon monoxide and carbon dioxide at stagnation conditions above their critical point have been investigated by time-of-flight measurements as a function of pressure and temperature1. Surprisingly large speed ratios (above 100) have been achieved that are indicative of very low translational temperatures (≤0.1 K). In particular, the supersonic expansion of CO2 at stagnation temperatures slightly above the phase transition to the supercritical state results in unprecedented cold beams. This efficient cooling is attributed to the large values of the heat capacity ratio of supercritical fluids in close vicinity of their critical point.
1 Wolfgang Christen, Klaus Rademann, Uzi Even, J. Chem. Phys. 125, 174307 (2006).