Düsseldorf 2007 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 22: Cold Molecules I (gemeinsam mit Q)

MO 22.4: Vortrag

Dienstag, 20. März 2007, 11:30–11:45, 6B

Photodetachment of cold OH⁻ in a multipole ion trap — •Sebastian Trippel, Jochen Mikosch, Raphael Berhane, Rico Otto, Matthias Weidemüller, and Roland Wester — Physikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

Negative ion photodetachment is the basis of many photoelectron spectroscopy studies. It is also a fundamental destruction process for negative ions in the environment. We have developed a method to deterimine the absolute photodetachment cross section of negative ions using a 22-pole radiofrequency ion trap. Previous studies have shown that these traps are well suited for collisional cooling of molecular vibrational and rotational states. In this work we present results for the photodetachment of trapped OH⁻ ions at 170 K rotational temperature. We obtain the absolute cross section in a direct and model-independent approach by measuring the decay constant of the trapped ions due to photodetachment. The density of ions interacting with the laser is measured in a tomography scan through the trap. In comparison with previous results, the cross section shows a sensitive dependence on the initial rotational state distribution. These results indicate that the rotational state dependence of the cross section is given by (2J+1), where J is the rotational quantum number of OH⁻. This rotational-state dependence might be relevant for models of the abundance of negative ions in the atmosphere or in interstellar space.

[1] S. Trippel et al., Phys. Rev. Lett. 97, 193003 (2006)