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Faculty of Mathematics and Natural SciencesAstrophysik I.Physik

Action Spectroscopy

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Investigators

  • Oskar Asvany
  • Thomas Salomon
  • Sven Thorwirth
  • Philipp Schmid
  • Divita Gupta
  • Mariyam Fatima
  • Weslley Silva
  • Marcel Bast
  • Eline Plaar
  • Julian Böing
  • Carsten Czapczyk

Description

The first detection of an ion, CH+, in the interstellar medium came about in 1941 as the features observed in 1937 were confirmed by the laboratory observation of these lines. Since then, almost 30 ionic species have been detected in the interstellar medium. The role of laboratory measurements over the years has been well established. Molecular ions are long known to be key intermediates in the chemical evolution in space. Their key role in driving chemistry in the interstellar medium is significant because their reactions are usually exothermic as the attractive potentials they induce increase reaction rates. Understanding their structures and reactivities, thus, forms a crucial component of experimental astrophysics.

Methods

In this lab, we perform spectroscopic measurements of many of these ions and other systems of fundamental importance, including potential astrochemical targets. We employ a variety of light sources including infrared lasers, mm-wave sources, etc. to measure their rovibrational and rotational spectra.

Ions are a challenging system to work with as they are highly reactive and difficult to be produced in large quantities. Special techniques are employed to generate them in-situ, which are later trapped in a cold 22-pole trap. Given the lower number of ions generally produced, a technique known as action spectroscopy is employed to measure the spectrum.

In this method, the spectrum is recorded not by detecting the absorption or emission of light by the molecules, but by the action of the light on the molecules, e.g., photon-induced dissociation of a chemical bond, a photon-triggered reaction, or photo-detachment of an electron. Action spectroscopy is by far the most sensitive technique and has developed into a versatile tool in the full spectral range of molecular spectroscopy, covering rotational, vibrational and electronic motion. The free electron laser at Nijmegen (FELIX) coupled with an ion-trap has also been employed by the group to measure vibrational spectrum.

We have also employed this technique to understand molecular dimers and helium complexes with ions. This technique can also be adapted to measure reaction rates of ions trapped with a neutral partner. These reactions remain fast at low temperatures (down to 10 K) and the measured reaction rates are crucial parameters for astrochemical modeling.

Selected Publications

Acknowledgments

This work is supported by the European Research Council Advanced Grant Project “MissIons”, Deutsche Forschungsgemeinschaft (DFG) through project (Grant No. SCHL 341/17-1), through the core facility project “Cologne Center for THz Spectroscopy” (Grant No. SCHL 341/15-1), the DFG via Grant No. SFB 956/III in project B2.