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Welcome to the High-Frequency EPR Group of the Institute of Problems of Chemical Physics, Russian Academy of Sciences. We respect it as a facility connecting scientists dealing with a study of various low-dimensional systems. Please find here the points converging the activity of the Group. We hope frankly that the information presented will appear to be useful for you.
Generally, we study biological and organic conducting macromolecules by using mainly multifrequency Electron Paramagnetic Resonance (EPR) method.
EPR method allows to determine molecular, conformational and relaxation features of different condensed system with unpaired electrons. If, however, the system contains two or more paramagnetic centers with close magnetic parameters, their spectra look as one spectrum at low registration frequency. Analogous problems are happened in case of paramagnetic centers with low anisotropic magnetic parameters. This is a reason that the last decades are characterized by a vast development of EPR spectroscopy of millimeter and submillimeter wavebands, which was proved to be more promising in the study of various condensed systems. In contrast with usually used 3-cm, 8-mm or even 3-mm waveband EPR techniques, 2-mm waveband EPR spectroscopy has some advantages.
The main advantage of the millimeter EPR method is higher spectral resolution over g-factor, which is just proportional to registration frequency or to external magnetic field. This feature is used for investigation of structure, polarity and dynamics of radical microenvironment in various spin-modified organic and biological systems.
The saturation of paramagnetic centers at comparatively low microwave polarizing field coming from the exponential dependence of number of excited spins on the registration frequency. Such effect is successfully used for a study of relaxation and dynamics of paramagnetic centers as well as of superslow motion in the systems under study.
The cross-relaxation of paramagnetic centers decreases dramatically at high magnetic fields, so then it is possible to obtain more precise and complete information about the system under study.
Increase in orientation selectivity in the investigation of disordered systems.
Accessibility of spin systems with larger zero-field splitting due to the larger microwave quantum energy.
Simplification of spectra due to the reduction of second-order effects at high fields.
The informativity and precision of pulse methods, e.g. ENDOR are also increase at high magnetic fields.
Above Figure shows how the spectral resolution of the method increases at the increase of precession frequency at registration of simplest nitroxide radical with anisotropic both g-factor and huperfine A-constant. The spectra calculated for standard wavebands EPR are shown by red lines. Main magnetic parameters of various nitroxide radicals determined experimentally are summarized in this Table. The g-factor standards used in the high-frequency/field EPR spectroscopy are summarized in this page.
The first 2-mm waveband EPR spectrometer elaborated using the concepts of Prof. Y.S. Lebedev, Russian Institute of Chemical Physics allowed to start a study of organic radicals in various condensed systems (solutions, polymers, crystals, etc.) in which complex molecular and relaxation processes proceed, including slow anisotropic motions, cross-relaxation, etc. This became the reason for the rise of the enthusiasm among scientists, which was accompanied by an explosive development of various method's application. However, the present tendency consists in that the main advantage of 2-mm EPR spectroscopy is not its successful application but the possibility to obtain a qualitative new information on the well-known compounds and to understand various phenomena, from specific interactions and correlated relaxation in condensed media to charge transfer in biological systems and organic semiconductors. 2-mm waveband EPR spectroscopy was shown to allow solving various practical problems in physics, chemistry, molecular biology and the problems, lying between these main branches of sciences. The spectral resolution, achieved at 2-mm waveband EPR, is quite enough for a separate registration of individual spectral lines of most organic free radicals with different structure and/or orientation in a magnetic field. The method enables one to obtain more correct and complete information on molecular and electron processes, realized in condensed systems. A higher spectral resolution provides the possibility to obtain qualitatively new information on metrology of free radicals, molecular dynamics and electron mobility, electron and dimensional structure of paramagnetic centers, matrix's local properties, etc. These data can be used for development of various components of molecular electronics.