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Numerical simulation of ESR spectra of nitrixides as a method of investigation. Andrey Kh. Vorobiev Moscow State University. Typical result of simulation of single ESR spectrum: qualitative accordance; small deviations from experiment. SiON(O ) CD 3. Rus.Chem Bull.V.50, No.12, p.2384. - PowerPoint PPT Presentation
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Numerical simulation of ESR spectra of nitrixides as a method of
investigation.Andrey Kh. VorobievMoscow State University
Typical result of simulation of single ESR spectrum: qualitative accordance;small deviations from experiment.
Rus.Chem Bull.V.50, No.12, p.2384
SiON(O ) CD3
Typical result of simulation of temperaturedependence of ESR spectrum: simulation of one spectrum is satisfactory;deviations from experiment are more then experimental noise.
Practice shows that for quantitative and reliablesimulation is necessary:
0. Quality of spectra recorded (subtract base line, avoid overmodulation, saturation, etc.);
1. Simulation of a set spectra (temperature dependence, angular dependence etc).;
2. Variation of parameters using least-squire minimisation method. (It gives impartial verification of your hypothesis) .
Proposed thesisProposed thesis: QuantitativeQuantitative modelling of spectra modelling of spectra produces more reliable and informative resultsproduces more reliable and informative results
Term "Quantitative modelling" means coincidence of experimental and calculated spectra within experimental errors.
Anisotropic line width is often necessary
convolution of isotropic Gauss and Lorentz lines
convolution of axial Gauss and Lorentz lines
G=7.2GL=0.71G
GX=7.9G, GZ=4.9GLX=0.21G, LZ=1.4G
exper.calc.
Distribution on magnetic parameters prevent to quantitative simulation
TEMPON in polystyrene 110K
Example:
Admixture of species with other magnetic parametersgives marked component.
Essential trouble for simulation: distribution on mobility
TEMPON absorbed on Na-mordenite in presence of water vapor
Experimantal spectrum consist of:
rigid limit spectrum,
spectrum of slow rotation
spectrum of fast rotation
Example:
Example of set of ESR spectra:Temperature dependence.
TEMPON in porous teflon AF-2400
100-150K
150-300K
300-400K
Experimental spectra:
Attempt of simulation using model of anisotropic Brownian rotation:
Deviations are more then experimental errors!
High temperature part of dependence
Simulation of the same spectra using model of simultanious isotropic rotation and anisotropic quasilibrations of probe:
Conclusion: quantitative simulation gives additional information even in the case of low-
informative spectra
Quasilibration: avereging on frequency, limited on amplitude moves.
Moves around three axes should be taken into account in general.
Results for whole temperature dependence:movements of probes in polyvinyltrimethylsilane
N OO
We thank Prof. Kalman Hideg and Dr.Tamas Kalaifor the gift of this substance.
Probe in liquid crystal 77K
Example of simulation of set of ESR spectra:Angular dependence of ESR spectrum.
Quantitative modelling of angular dependence gives the orientation
distribution function:
X
Y
Z
X
Distribution function is presented in molecular frame
A.Kh.Vorobiev, N.A.Chumakova,J.Magn.Res. 2005, 175, No.1 pp.146
Relaxation of orientation distribution function at the annealing
X
Y
Z
X X
Y
Z
X
X
Y
Z
X X
Y
Z
X
77К 195К
226К 236К
Orientation of probe molecule relative to liquid crystal are determined by quntitative simulation of spectra.
Dr. Vladimir GurmanDr. Tatiana Klimenko Natalia Chumakova Daria Chernovatook part on presented work