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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


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.


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.


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.


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), [4]. 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.


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, [5]. The interconnecting aim of these two aspects is devoted to improve the understanding of the formation of molecules, larger clusters and nano particles, [6]. 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 [7]. Habilitation at the Technical University Chemnitz, title of the thesis: "Molecular reaction dynamics - gas phase, clusters and nanoparticles".


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

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.

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, 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.

Recently we were successfull in detecting the first gas phase IR spectrum of CH5+[8] and during the last months also the first pure rotational transitions in H2D+ and D2H+ [9]. Currently we are starting to understand the origin of deuterium fractionation in space and laboratory. The development of new experimental techniques in spectroscopy [10] and molecular collisions is the driving force for the science carried out in my group.

Author of more than 60 peer reviewed publications, more than 50 invited talks and contributions to international conferences in the last five years. Principle investigator of several research grants (12 past, 3 present and 3 pending). Supervision of 9 diploma thesis (2 current), as well as 6 curent and 6 past Ph.D. thesis. Organization of several international conferences and meetings. Host of several DAAD fellows.

Awards and Prizes

1986 Diploma work with award of the grade "Mit Auszeichnung" (summa cum laude).
1986-1989 Stipend of the Max-Planck society for doctoral work
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
2009 Guest Professorship at Universite Paul Sabatier in Toulouse (Host: Christine Joblin)
2009 Morino-Lecture in Japan
2011 Guest Professorship at Universite Paul Sabatier in Toulouse

Scientific education

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

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)

Title: "Hochaufgelöste Molekularstrahluntersuchungen der inelastischen und reaktiven Streuung kleiner Moleküle"

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