Darmstadt 2008 – scientific programme

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MO: Fachverband Molekülphysik

MO 10: Kalte Moleküle III (gemeinsam mit Q)

MO 10.2: Talk

Tuesday, March 11, 2008, 14:15–14:30, 3G

Internal-state thermometry by depletion spectroscopy in a cold guided beam of formaldehyde — •Michael Motsch, Markus Schenk, Laurens D. van Buuren, Martin Zeppenfeld, Pepijn W.H. Pinkse, and Gerhard Rempe — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany

Velocity filtering by means of an electrostatic quadrupole guide is an efficient technique to produce slow beams of polar molecules from a thermal reservoir. For formaldehyde, fluxes of 10¹⁰ s⁻¹ with velocities down to ∼10 m/s have been demonstrated [1]. However, so far the internal-state distribution of the velocity filtered molecules was not accessible in the experiment.

We present measurements of the internal-state distribution of electrostatically guided formaldehyde [2]. Upon excitation with continuously tunable ultraviolet laser light, molecules can be excited to a dissociating state, leading to a decrease in the molecular flux. The population of individual guided states is measured by addressing transitions originating from them. The measured populations of selected states show good agreement with theoretical calculations for different temperatures of the molecule reservoir. The purity of the guided beam as deduced from the entropy of the guided sample using a reservoir temperature of 150 K corresponds to that of a thermal ensemble with a temperature of about 30 K.

[1] S.A. Rangwala et al., Phys. Rev. A 67, 043406 (2003)

[2] M. Motsch et al., arXiv:chem-phys 0710.3316v1 (2007), accepted for publication in Phys. Rev. A