Physical and chemical properties of condensed phase matter are often determined by non-bonded intermolecular interactions, such as van der Waals interactions and hydrogen bonding. A fundamental description of these macroscopic properties requires detailed knowledge about the corresponding microscopic interactions, i.e., interactions on the molecular level. Similarly, certain biological processes, such as protein folding and molecular recognition, can be regarded as the concerted action of many microscopic site interactions.
A prerequisite for exploring and understanding the link between molecular interactions and macroscopic properties is the availability of accurate potential energy surfaces for binary interactions. A further step is then the investigation of ternary - systems in order to extract information about non-pairwise additive contributions to the interaction energy. The most detailed and accurate experimental information about such interactions can be obtained using spectroscopic methods.
The research objective is the investigation of rotational and ro-vibrational spectra of binary and ternary van der Waals complexes. The complexes are formed in a pulsed supersonic molecular expansion and then subjected to a microwave excitation pulse. The resulting molecular coherent spontaneous emission signal ("super-radiation", "free-induction-decay") is A/D-converted and stored in a fast transient recorder. A Fourier transformation of the time-domain signal gives the frequency spectrum. Intermolecular vibrational transitions are detected with a newly developed double resonance technique, using Terahertz radiation sources.
The research offers the opportunity to be involved in a diverse range of areas: from development and use of state-of-the-art scientific instrumentation, computer programming for experiment control and spectral analyses to syntheses of isotopically labelled compounds.
Potential energy surface of an atom-diatom system (e.g. Ne-N2). The rotational and rovibrational spectra are sensitive fingerprints of the well region.
Q. Wen and W. Jäger, "Rotational Spectra of the Xe-(H2O)2 van der Waals Trimer: Xenon as a Probe of Electronic Structure and Dynamics", J. Phys. Chem. A 2007, 111, 2093-2097.
A. R. W. McKellar, Yunjie Xu, and Wolfgang Jäger, "Spectroscopic Exploration of Atomic Scale Superfluidity in Doped Helium Nanoclusters", Phys. Rev. Lett. 2006, 97, 183401-1 - 183401-4.
R. Lehnig and W. Jäger, "Infrared spectroscopy of the antisymmetric stretching mode of 16OC18O in helium nanodroplets", Chem. Phys. Lett. 2006, 424, 146-150.
Y. Xu, W. Jäger, J. Tang, and A. R. W. McKellar, "Spectroscopic Studies of Quantum Solvation in HeN-N2O Clusters", Phys. Rev. Lett. 2003, 91, 163401-1 – 163401-4.
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