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Prof. Dr. Stephan Schlemmer

I. Physikalisches Institut
Universität zu Köln
Zülpicher Straße 77

Research Interests

  • Molecular Physics
  • Spectroscopy, specific projects: THz spectroscopy (superlattice spectrometer),
    mm spectroscopy (solid state spectrometer, intracavity OROTRON),
    IR spectroscopy (OPO laser system)
  • Collision Dynamics
  • Cold Collisions
  • Astrochemistry

Scientific life

Since October 2004

Professor of experimental physics at I. Phys. Institut, Universität zu Köln. Head of the laboratory astrophysics group.
Key words: High resolution millimeter and sub-mm spectroscopy, chirped pulse spectroscopy, emission spectroscopy, infrared spectroscopy, Cologne Database for Molecular Spectroscopy (CDMS), reaction kinetics and dynamics at low temperatures, ion-molecule reactions, laser induced reactions, transient species, jets and molecular beams.

May 2003- September2004

Associate professor at the Leiden Obsvatory. Focussing the research interests on astrochemistry. One gas‑phase experiment and two UHV surface science apparatus were used to conduct experiments simulating processes in the interstellar medium. The IR spectroscopy of molecular ions has been further developed and with the use of the free electron laser (FELIX) at FOM Rijnhuizen the full infrared range has been accessed.


Development of an independent research profile as an assistant professor (C2) in Chemnitz.


Scientific assistent in the group of Prof. D. Gerlich, Chemnitz. The work in Chemnitz has been focussed on two scientific areas, gas phase ion molecule reactions at low temperatures and the development of a method for high resolution mass determination of nano particles. The interconnecting aim of these two aspects is devoted to improve the understanding of the formation of molecules, larger clusters and nano particles. These investigations are carried out under extreme conditions, low temperature and low pressure. They are important in the area of material science and astrochemistry. During this time we developed a very sensitive technique for IR spectroscopy of mass selected ions which is also used to study the state-selective dynamics of bimolecular reactions. Habilitation at the Technical University Chemnitz, title of the thesis: "Molecular reaction dynamics - gas phase, clusters and nanoparticles".


Post-Doc at the University of California at Berkeley, USA, in the group of Prof. R.J. Saykally. My stay at Berekeley was devoted to the origin of the interstellar unidentified infrared bands (UIR). For that purpose we setup a laboratory experiment to test the so called PAH-hypothesis. According to this hypothesis polycyclic aromatic hydrocarbons (PAHs) are responsible for the IR emission features observed in a large variety of astrophysical environments. In the experiment we observed the IR-emission as a product of the rapid IVR and IC processes upon UV-radiation which resembled the excitation of the astrophysical molecules from a nearby star.


Post-Doc at the Universita di Perugia, Italy, in the group of Prof. P. Casavecchia. Installation of hardware as well as the software (own development) to implement the TOF-technique for chemical reactions in the Perugia group.


Scientific assistent at the Max-Planck-Institute for fluid dynamics in the group (Molecular Interaction) of Prof. J.P. Toennies. The main work included the operation of a crossed molecular beam apparatus for the investigation of rotationally inelastic and reactive collisions. Rotationally partially resolved time-of-flight (TOF) spectra of products from the F+H2 reaction have been recorded for the first time. The major aim of this work was to obtain high-resolution data to unravel the dynamics of molecular collisions.


As an undergraduate I took part in the development of a revolutionary technique to prepare the surface of a volatile liquid for investigations using surface science techniques in ultra-high vacuum.

Awards and Prizes

2021 International Dr. Barbara Mez-Starck Prize, Dr. Barbara Mez-Starck Foundation
2021 ERC Advanced Grant
2015 Gay-Lussac-Humboldt Prize, French Ministry for Education and Research
2011 Guest Professorship at Universite Paul Sabatier in Toulouse
2009 Guest Professorship at Universite Paul Sabatier in Toulouse (Host: Christine Joblin)
2009 Morino-Lecture in Japan
1992-1994 Research stipend of the German-Science Foundation for post doctoral work in Berkeley
1992 Otto-Hahn Medal of Max-Planck-Society for PhD work
1986-1989 Stipend of the Max-Planck society for doctoral work
1986 Diploma work with award of the grade "Mit Auszeichnung" (summa cum laude)

Scientific education

Diplom Physiker (Georg August University, Göttingen, Dipl. Phys.) (4/1986)

Thesis title: "Molekularstrahluntersuchungen des Verdampfungsprozesses von H2O‑Molekülen aus der Oberfläche sehr dünner Wasserstrahlen"

Molecular investigations of the evaporation process of water molecules from a surface of a very thin liquid jet

Doktor (Georg August University, Göttingen, Dr.rer.nat) (7/1991)

Thesis title: "Hochaufgelöste Molekularstrahluntersuchungen der inelastischen und reaktiven Streuung kleiner Moleküle"

High-resolution investigations of inelastic and reactive scattering of small molecules

Habilitation (Technical University Chemnitz, Dr. habil.) (6/2001)

Thesis title: "Molecular reaction dynamics - gas phase, clusters and nanoparticles"