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Electron paramagnetic resonance (EPR)
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| Electron paramagnetic resonance (EPR) is the name given to the process
of resonant absorption of microwave radiation by paramagnetic ions or molecules,
with at least one unpaired electron spin, and in the presence of a static
magnetic field. EPR was discovered by Zavoisky in 1945. It has a wide range
of applications in chemistry, physics, biology, and medicine: it may be
used to probe the "static" structure of solid and liquid systems, and is
also very useful in investigating dynamic processes. |
Research Activities
| Electron Paramagnetic Resonance (EPR) Spectroscopy is well known to
provide detailed informations with high sensitivity of paramagnetic species.
Particulary, EPR offers the possibility to study the molecular
structure, the kinetics and the conformational analysis of organic
radicals. In addition, measurements of EPR spectra at various temperatures
allow the determination of potential barriers between different conformations. |
| Our research interests are focused both on investigations of organic
radicals in solution as well as on free radicals in solid polymer systems.
The radicals in solution are generated in situ via photolysis of di-t-butyl
peroxid. In situ generation of radicals in solid polymer systems succeeds
by direct photolysis and radiolysis of the sample, respectively. |
| Substituted heteroallyl radicals and macroradicals are subject of our
studies of organic radicals in solution. For example, the analysis of the
EPR spectra of 2-phenyl substituted heteroallyl radicals yields detailed
informations of their molecular structure. Different substituents often
have great influence on the spin distribution in the radicals, going along
with specific changes in the spectra. |
| Dynamic processes like hindered rotation in the radicals may cause
line shape effects. According to the temperature dependence of the spectra,
the observed lines assigne to individual conformations and the dynamics
of their interconversions. In the course of this study, the conformational
analysis of macroradicals is another subject we are intersted in. Furthermore,
the comparison of experimental measured hyperfine coupling constants with
theoretical calculations is of great importance to check theoretical predictions.
The cooperations with Prof.
Dr. B. Engels, Institute of Theoretical Chemistry, University
of Bonn, now at Würzburg, complete our investigations in understanding
the molecular structure of radicals and their dynamics. |
| In addition, our interest of research is thephoto
and radiation chemistry of solid polymer systems. These
investigations include besides EPR spectroscopy different spectroscopic
methods, for example mass spectroscopy and the use of quartz microbalance.
Tools for radical generation are a 1 kW high pressure mercury-xenon short
arc lamp, LASER and synchrotron radiation. The combination of synchrotron
radiation and EPR spectroscopy represents a new powerful device for in
situ investigations of the behaviour of organic molecules under X-ray exposure. |
Contact: Franz-Josef Hünerbein
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