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Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Research Projects

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  • asvany
  • toepfer
  • schlemmer


The ion CH3+ and its isotopologues are of astrophysical interest, because they transport deuterium from HD into larger molecules, starting with the exothermic reactions:
  • CH3+ + HD ⇌ CH2D+ + H + E
  • CH2D+ + HD ⇌ CD2H+ + H + E
  • CD2H+ + HD ⇌ CD3+ + H + E
As ions are very reactive and it is energetically preferable to have deuterium in the larger one of two reaction partners, deuterium is easily transferred to heavier molecules from the CH3+ isotopologues. For this reason, the CH3+ isotopologues have been investigated spectroscopically before and there were continued efforts to detect them in the interstellar medium. The tentative detection of CH2D+ in Orion IRc2 resulted in new efforts to improve the precision of predictions for pure rotational transitions of CH2D+. ...more


Laser induced reactions (LIR)
Laser induced reactions (LIR) belong to the family of "action spectroscopy" methods. 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 performing 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.
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The 22-pole ion trap apparatus LIRTrap is used both for kinetic and spectroscopic characterization of ions.
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COLTRAP and FELion are two new generation 22-pole ion trap instruments developed and built in our laboratory. Both instruments offer unique possibilities to study the kinetics of ion-molecule reactions at low temperatures, and to use highly sensitive methods for spectroscopic studies of molecular ions. Whereas the COLTRAP instrument is located in the Cologne laboratories, FELion has been installed in October 2014 at the FELIX Laboratory (Radboud University Nijmegen, Netherlands).
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Recent Results

One of the 21 pure rotational lines of CH2D+ measured with the double resonance rotational method.
112 rovibrational transitions of CH2D+ have been observed (ν1 and ν4 branch), leading to predictions of pure rotational transitions with MHz accuracy. The observed line positions and global fits can be found in the CDMS.

Simulation of the vibrational bands ν1 and ν4 of CH2D+.
Example of an observed spectrum of CH2D+.

A reference spectrum of OCS was recorded simultaneously for frequency calibration.


External Links


  • Funding by SFB 956 B2.