Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Aufbau eines Radiofrequenzgenerators

(Betreuer: O. Asvany, L. Kluge)

Inhomogene Radiofrequenzfelder werden in Ionenspeichern zur  Zur Speicherung

Charakterisierung einer Elektronenkanone

(Betreuer: O. Asvany)

Eine Elektronenkanone dient zur Erzeugung monochromatischer Elektronen.
Mittels Steuerelektroden kann die Energie der Elektronen eingestellt werden und der Strahl im Raum geformt und gelenkt werden.
Die vorhandene Elektronenkanone ist eine Verbesserung der in der Literatur beschriebenen Kanone von Erdmann und Zipf.
In einem späteren Experiment soll die Elektronenquelle zur gezielten Ionisierung eines Gases verwendet werden.
Ziel der Arbeit ist eine Charakterisierung der Elektronenquelle: 
Beschreibung des Vakuum-Messaufbaus und der Elektronenquelle
Simulation von Trajektorien der Elektronen
Messung der Intensität bzw. Stromdichte und der Strahlenergieverteilung.

Temperatur-/Kalibrationsmessungen am Lirtrap-Experiment

Laser induced reactions (LIR) belong to the family of "action spectroscopy" methods where the influence of the laser light on the investigated mass-selected trapped ions is monitored by detecting induced changes of the ion cloud composition in a high-efficiency ion counter. In the special case of LIR, changes of the rate coefficient of an endothermic ion-molecule reaction serve to detect the excitation of the parent ionic species. This offers not only the possibility of doing very high sensitivity spectroscopy on transient ions (a number of only 1000 ions per trapping period is enough), but LIR can yield information on state-selected reaction rate coefficients and lifetimes of excited states.

Contact: Prof. Dr. Stephan Schlemmer


Cold molecular ions

The objective of this project is the determination of IR and FIR spectra of molecular ions as well as the quantitative understanding of the dynamics of ion molecule reactions at temperatures relevant to the interstellar medium. In a 22-pole ion trap apparatus the rather specific and ultra-sensitive method of laser induced reactions (LIR) is applied to obtain spectra for small hydrocarbon ions as well as for the astrophysically relevant H2D+. Recent developments in our laboratory aim at the possibility to obtain also spectra of the rather elusive polycyclic aromatic hydrocarbon (PAH) molecules, which are thought to be one of the most important carbon carriers.

Contact: Prof. Dr. Stephan Schlemmer


Many complex molecules are found in molecular clouds and in star forming regions in particular. Understanding their formation is one of the key questions in astrochemistry. Another is how complex can those structures be depending on the actual astrophysical environment, in particular whether being in high and low mass star forming regions. Molecules can be formed mainly via gas phase reactions of ions with neutrals or via surface reaction mechanisms. Presently fairly complex scenarios are considered where some less complex molecules are formed in gas-phase, freeze-out on grains, surface-react, desorb and potentially react further in the gas phase. Observations of particular molecules which are thought to be related in particular reaction schemes can give clues as to what the dominant formation process is.

Many of the complex molecules like ethanol, C2H5OH, can be identified by their rotational lines of the main isotopologue which in many cases are available in Cologne Data Base for Molecular Spectroscopy (CDMS). However, dimethyl ether, CH3OCH3, is an example of a very prominent molecule in space, for which not even this information is available over a sufficient frequency range and thus many astronomical line surveys suffer from the presence of unidentified lines. It is the aim of current projects in the THz spectroscopy group to fix this problem thanks to very high-accuracy measurements in the laboratory.

Contact:Dr. Frank Lewen