Jan Peter Toennies (born 3 May 1930) is a German-American scientist, known for his contributions to molecular physics, surface scattering, and the development of helium nanodroplet spectroscopy.

Early life and education

Toennies was born in Philadelphia, Pennsylvania on 3 May 1930 to German immigrant parents. as well as a guest professor in the Department of Physical Chemistry at the Gothenburg University. In 1969 he became director at the Max Planck Institute for Fluid Dynamics. From 1971 he was a professor in Göttingen and honorary professor at the University of Bonn. He retired officially in 1998, but was acting director until 2004. He investigated vibrational excitation of H<sub>2</sub> in central collisions with Lithium ions using the time-of-flight method, as well as dissociation in single collision events. In Göttingen, his group solved the Boltzmann equation while accounting for quantum effects and realistic interaction potentials in helium free-jet expansion, and proposed an improved model for van der Waals potential, referred to as Tang-Toennies model. High-resolution measurements of surface phonon dispersion for Ag, LiF, NaF, KCl, and Pt-crystals were carried out using inelastic scattering of helium atoms. The group achieved non-destructive detection of fragile He, H<sub>2</sub> and D<sub>2</sub> clusters by utilizing diffraction from nanoscopic transmission gratings. A spectroscopic study of SF<sub>6</sub> doped in helium nanodroplets revealed sharp spectral features of the embedded molecule. This indicated that the molecule was extremely cold and that it resides in its ground state at a temperature of 0.37 K, practically unaffected by the helium environment and could rotate freely as if in a vacuum. Subsequent spectroscopic experiments demonstrated that the free rotations were related to the microscopic superfluidity of helium droplets, and, for the first time, of a small numbers of hydrogen molecules.

Monographs

  • E. F. Greene and J. Peter Toennies: Chemische Reaktionen in Stoßwellen, Dr. Dietrich Steinkopff Verlag, Darmstadt, 1959
  • E. F. Greene and J. Peter Toennies: Chemical Reactions in Shock Waves, Edward Arnold (Publishers) Ltd. London, 1964
  • G. Benedek and J. Peter Toennies: Atomic Scale Dynamics at Surfaces: Theory and Experimental Studies with Helium Atom Scattering, Springer, Heidelberg, 2018
  • A. Slenczka and J. Peter Toennies: Molecules in Superfluid Helium Nanodroplets: Spectroscopy, Structure, and Dynamics, Springer Cham, 2022

References

Further reading