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Universität zu Köln
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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Instruments

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SURFER - A laboratory heterodyne emission spectrometer at submillimeter wavelengths (300 - 400 GHz)

The quantum limited SIS-mixer (300 - 400 GHz)was designed and manufactured in-house within the SFB-D3 subproject (Netty Honingh, Karl Jacobs, Michael Schultz). Implementation of the detector electronics and design of the intermediate frequency processor was accomplished within the SFB-S subproject (Urs Graf and Bernhard Schmidt). Furthermore, the dewar housing, design of the thermal link to the SIS detector, the cryogenic shielding and the optical path were also designed within the SFB-S subproject (Henning Adams, and Ph.D. student Norma Hurtado for the design of the thermal link). First test experiments at 800 GHz were performed by Alexey Potapov. Final tests and proof-of-concept by taking very first spectra of complex organic molecules were carried out by Nadine Wehres and Jakob Maßen (Master student). Verification of absolute intensities reflecting local thermodynamic equilibrium was accomplished by comparing the experimental spectra to an XCLASS/MAGIX simulation, a computer code used to simulate the rotational spectra of telescope data. The simulation has been obtained Kirill Borisov; his Ph.D. project is shared between the B and C3 sub-projects. The accepted manuscript can be found under: Physical Chemistry Chemical Physics, 2017, DOI: 10.1039/C7CP06394F
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Carbon Cluster Experiment

In the carbon cluster experiment, part of the infrared probe radiation is guided through a reference gas cell and a reference interferometer for calibration purposes. The major fraction is guided into a vacuum chamber and through a Herriott-type multireflection cell where it is intersecting the free jet harboring the clusters perpendicularly close to the exit of a slit nozzle. After having passed the chamber, the infrared beam is detected using sensitive InSb or HgCdTe detectors and its signal is digitized using an USB oscilloscope.
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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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Cologne Spectrometer for cold Molecules in Interstellar Clouds (COSMIC)


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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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LIRTrap

The 22-pole ion trap apparatus LIRTrap is used both for kinetic and spectroscopic characterization of ions.
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MIDAS-COINS

With its exceptionally long absorption path, MIDAS-COINS is enhancing our sensitivity in the millimeter range since 2010.
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OROTRON

The OROTRON spectrometer has become the most sensitive and probably the most powerful tool for investigating inherently extremely weak spectral features of molecular complexes and small clusters in the millimeter-wave (MMW) range [L.A. Surin, et.al.Rev. Sci. Instrum., 72, 2535 (2001)]. The key element of the spectrometer is a tunable OROTRON oscillator, which generates the radiation (2-3 mm) through the interaction of an electron beam with the electromagnetic field of an open Fabry-Perot resonant cavity. The supersonic molecular jet enters into the resonator perpendicularly to its axis. A high quality factor (Q ≈ 104) of the cavity results in 100 effective passes of the radiation through the jet. Absorption in the cavity causes changes of the electron current in the collector circuit and is detected by measuring these current changes.
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Para-Hydrogen Converter

Molecular hydrogen can exist in two different nuclear spin configurations, named "ortho" and "para". The difference between these two configurations is the symmetry of the nuclear wave function. The effect of this difference can be seen in the rotational energy of the molecule. Due to symmetry reasons the rotational ground state of hydrogen can only be occupied by para hydrogen molecules, while the lowest possible state for ortho hydrogen is the first excited rotational state. For the investigation of reactions relevant to astrochemistry, it is important to perform experiments at low temperatures. At these temperatures the rotational energy from the first excited rotational state often is sufficient to change the equilibrium of the observed reaction. Therefore, astrochemical experiments often need high quality para hydrogen. As hydrogen naturally comes with an ortho to para ratio of 3/1 ("normal" hydrogen) on earth, a reliable conversion method is needed. As part of the SFB 956 project B2 the cologne para hydrogen converter was modified to allow the production of higher amounts of para hydrogen, which contain almost the natural abundance of deuterium. The higher amount of para hydrogen enables Raman spectroscopy as a test method for the purity, the higher amount of deuterium makes chemical tests of the purity in the ion trap more reliable.
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Para-Hydrogen Converter

For the conversion of ortho hydrogen into para hydrogen two environmetal conditions are necessary: The environment has to be cooled down below 20 K and a paramagnetic catalyst material has to present. The low temperature shifts the equilibrium of energy level occupancy to almost 100 % of para hydrogen (rotational ground state). The paramagnetic catalyst enables the spin flip of the molecules from ortho to para hydrogen. There are several methods how to bring the hydrogen into and out of this conversion environment.
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100 GHz room-temperature emission spectrometer

The modern developments of highly sensitive room-temperature low-noise amplifiers in combination with room-temperature mixers as well as advances in digital Fast Fourier transform spectrometers (FFTSs) for the space and ground observatories make also laboratory emission spectroscopy very attractive, in the light of the possibility of fast measurements of high resolution broadband spectra with high sensitivity and precise line intensities. Thus, emission spectroscopy is of interest for the spectroscopy itself, allowing fast broadband spectral measurements, and for the physical chemistry, providing measurements of absolute line intensities and shapes.
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The Cologne Terahertz Spectrometer

In Cologne, high resolution, broadband scanning spectroscopy with microwave accuracy has been extended into the terahertz region (λ < 0.3 mm) by stabilization of continuously tunable backward wave oscillators (BWOs) from Russian fabrication. Precise measurements have been performed up to 1.3 THz, a frequency which has never been reached before directly using microwave techniques, i.e. without generation of harmonics.
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Waveguide Chirped-Pulse Experiment


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