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Universität zu Köln
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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Experimental Methods and corresponding Instruments

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Category: Spectroscopy / Ion Traps

Double resonance rotational action spectroscopy

The double resonance rotational action spectroscopy scheme is a method that can be used to bring well established rovibrational schemes to the pure rotational domain. It works on the principle of redistributing the rotational population of the studied molecule ensemble (1. photon, usually THz radiation), effectively influencing the second action spectroscopy method, responsible for the signal detection. Wide range of schemes can be applied as a second process e.g. laser induced reactions (LIR), the messenger tagging technique, or the infrared multiphoton dissociation (IRMPD).
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COLTRAP

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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Light Induced Inhibition of Complex Growth (LIICG) and Rotational State-Dependent Attachment of He Atoms

LIICG is a novel action-spectroscopy scheme (see also LIR - Laser Induced Reactions technique) for measuring high-resolution ro-vibrational spectra of gas-phase molecular ions. This method makes use of an inhibition of Helium-attachment to vibrationally excited molecular ions. Furthermore, we also observed a change in the rate of Helium-attachment depending on the rotational state of the cold, stored molecular ions. This effect can be exploited to perform purely rotational action spectroscopy on a wide class of molecular ions. Both methods can, due to the low temperatures needed, only be employed in our two new 4 K 22-pole ion traps COLTRAP and FELion.
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COLTRAP

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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FELion

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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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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LIRTrap

The 22-pole ion trap apparatus LIRTrap is used both for kinetic and spectroscopic characterization of ions.
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Reconstruction of Molecular Energy Levels Using Combination Differences: From Lines to states without a Model

For molecules which lack an appropriate model (as CH5+) common data evaluation methods which are based on the assignments of the measured lines to those of the model cannot be applied. Instead pattern recognition methods have to be applied to the measured data to reconstruct at least the energy levels of the molecule (without quantum numbers). Such a pattern recognition method is the Ritz combination principle which is more than 100 years old. It is based on calculating all possible CDs from the measured lines and searching for cumulationg values. This method has been enhanced a lot to be reliably applicable even to very dense spectra as that of CH5+.
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