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Sub-project E: Prof. Dr. K. Kleinermanns

Universität Düsseldorf


Stepwise Aggregation of Small Molecules in a Gas Jet: From Dimers to the Building Blocks of Seed Crystals

It is the objective of subproject-E to spectroscopically investigate the structural motifs of cocrystals and the kinetics of their formation. Nanocrystals in a supersonic gas jet act as a model system for the investigation of seed crystals. Mass and isomer selective ionization spectroscopy and dispersive fluorescence spectroscopy are used for the characterization of clusters.  Especially complex aromatic clusters like benzene, fluorobenzene, phenol or pyrazine with acetylene and acetone with acetylene are in the focus of our interest.

REMPI spectrum of the pyrazine dimers measured on the mass channel of the dimer.

Method: Clusters are formed in the gas jet by adiabatic cooling down to a few Kelvin. Analysis is done by resonant ionization of e.g. benzene-acetylene clusters using IR-UV and UV-UV double resonance spectroscopy. The relative cluster energy of different isomers and the kinetics of their formation are determined by varying the expansion conditions and the expansion temperature. The influence of aromatic-acetylene cations on the efficiency of building seed crystals is a further topic of interest. A high resolution IR-OPO system (linewidth ≤ 0.1 cm-1) is used to discriminate between closely neighboured spectral features of different cluster isomers.