Properties
and intermolecular (intracluster) reactions of molecular aggregates
Molecular
aggregates are suitable modell systems for investigations of the influence
of intermolecular interactions on the properties of molecules. The aggregates
form the smallest subunits in macroscopic systems like liquids, solution
or crystalls. In the laboratory scale they are formed by adiabatic expansion
of gas mixtures.
The
main goals of our investigations are the evaluation of structures and intermolecular
binding energies of these aggregates and their reactivity. We investigate
aggregates (clusters) formed by small aromatic molecules and solvens molecules
(eg. NH3, H2O,
alcohols). Typical intracluster reactions are electron and proton transfer,
aromatic substitution reactions and oxidations. Size and composition of
the aggregates determine the reaction mechanisms.
Molecular
aggregates were investigated by PIMS, REMPI and REMPI-PES (both with one
or two color excitation) and fluorescence spectroscopy. Different ns-laser
systems (Nd-YAG- and dye lasers, resolution up to 0.01 cm-1)
and molecular beam apparatus are available. Investigations which demand
high resolution or ultra fast laser systems are performed in cooperation
with the European Laboratory for non Linear Spectroscopy (LENS)
in Florence/Italy (S. Califano)
or the Max-Born-Institut
(I. V. Hertel) in Berlin/Germany.
The interpretation of the experimental results is supported by ab initiocalculations
in cooperation with Dr.
M. Oppel (AG
Manz FUB).
Current
topic: Intracluster reactions of aromatic molecules and nitrogen oxides.
Contact
persons: Sabine Marquardt
and Asnakech S. Gemechu
Additional
information
Spectroscopy
with synchrotron radiation
We
investigate isolated molecules and clusters. The Rydberg states of neutral
and ionic molecules were studied. Beside the spectrocopic properties the
unimolecular decay of the molecular ions were investigated.
Absorption
spectroscopy, PIMS, PES, fluorescence spectroscopy and coincidence techniques
were used.
Topics
are the determination of spectroscopic and thermodynamic data and the understanding
of unimolecular decay mechanisms of the molecular ions. An important goal
is also the investigation of systems witch appear in space and circumstellar
atmospheres. At present a new experimental setup (a combination of VUV-
and laser spectroscopy) is established. Scientific cooperations exist with
R. Locht (Lüttich), S. Leach (Paris) and R. Tuckett (Birmingham)).
Contact
person: Dr. H.-W. Jochims
Electrochemistry
and phase transition research
Organic
molecules are adsorbed at electrodes and change their electrochemical properties.
In addition those unstructured adsorbates show phase transitions forming
well structured phases. The topics of the research are the rate of the
phase transitions and the structure of the resulting phases. Beside standard
methods the measurement of current transients after potential jumps and
STM are used. A cooperation exists with U. Retter (BAM).
Contact
persons: Dr. Constanze Donner
and Stefanie Kirste
Research
on levitated microdroplets
An
apparatus was built to study the behaviour of levitated liquid microdroplets
in a temperature regime down to -90 °C. With this tool we are able
to look at the phase transitions, the gas uptake and the evaporation dynamics
of single droplets. Additional
information
Contact
persons: Peter Stöckel,
Juliane
Klein and Inez Weidinger