Darmstadt 2008 – scientific programme

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MO: Fachverband Molekülphysik

MO 10: Kalte Moleküle III (gemeinsam mit Q)

MO 10.3: Talk

Tuesday, March 11, 2008, 14:30–14:45, 3G

Cooling and Slowing in High Pressure Jet Expansions — •Wolfgang Christen and Klaus Rademann — Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin

The expression for the mean flow velocity in supersonic beams of ideal gases is extended to include real gas properties. This procedure yields an explicit dependence of the flow velocity on pressure, as observed in recent experiments of free jet expansions [1,2]. Applied to stagnation conditions slightly above the critical point, the model suggests that seeded high pressure jets might be suitable for slowing down virtually any molecule with high efficiency. Moreover, we discuss the consequence of a pressure-dependent flow velocity v₀ for the speed ratio S=v₀/Δ v_∥ with respect to collisional cooling and suggest to use the velocity spread Δ v_∥ as a more non-ambiguous measure of translational temperature in high pressure jet expansions.

[1] L. W. Bruch, W. Schöllkopf, J. P. Toennies, J. Chem. Phys. 117, 1544 (2002).

[2] W. Christen, T. Krause, K. Rademann, Rev. Sci. Instrum. 78, 073106 (2007).