CIDEP (chemical induced electron polarization) focus on the polarization
in the ESR spectra of photochemically produced species. This polarization
is named in analogy to the NMR chemically induced dynamic nuclear polarization
CIDNP.
A polarzied spectrum is one which reflects a non-Boltzmann distribution
of populations. The intensities of the spectra can correspond to
deviations from the Boltzmann equilibrium values of two orders of magnitude.
The polarization effect depends on the nature of the paramagnetic
system and the mechanisms of its formation. In some systems the whole spectrum
may be in emission, while for free radicals the excess population of the
upper levels may be selective for certain nuclear spin states, so that
some hyperfine lines appear in emission and some in enhanced absorption.
Free radicals in solution have spin-lattice relaxation times of the
order of microsecends, while for triplet states the values may, under certain
conditions, be even shorter. Thus the timescale for detecting of polarization
in the nanosecond region.
Although CIDEP can be detected under continous photolysis, we
use pulsed laser system (excimer laser) to produce radical pairs.
The CIDEP effect is used in our lab for the investigation of
homogeneous electron-self exchange reactions.
These reactions cause the individual changes of the hyperfine lines
from emission to absorption . From these changes the rates of the
bimolecular electron transfer can the deduced.
A CW-CIDEP-ESR spectrometer for the simulatanious detection of both,
CW- and CIDEP-spectra in currently under construction.
Fore more information on this subject, please contact Prof.
G. Grampp.