Numerical simulation of ESR spectra of nitrixides as a method of investigation.
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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.

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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: method of investigation. qualitative accordance; small deviations from experiment.

  • SiON(O) CD3

Rus.Chem Bull.V.50, No.12, p.2384


Typical result of simulation of temperature method of investigation.

dependence of ESR spectrum:simulation of one spectrum is satisfactory;deviations from experiment are more then experimental noise.


Proposed thesis method of investigation.: Quantitativemodelling of spectra

produces more reliable and informative results

Term "Quantitative modelling" means coincidence of experimental and calculated spectra within experimental errors.

Practice shows that for quantitative and reliable

simulation 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).


Anisotropic line width is often necessary
Anisotropic line width is often method of investigation.necessary

convolution of isotropic

Gauss and Lorentz lines

convolution of axial

Gauss and Lorentz lines

exper.

calc.

dGX=7.9G, dGZ=4.9G

dLX=0.21G, dLZ=1.4G

dG=7.2G

dL=0.71G


Distribution on magnetic parameters prevent to quantitative simulation
Distribution on magnetic parameters prevent to quantitative simulation

Example:

TEMPON in polystyrene 110K

Admixture of species with other magnetic parameters

gives marked component.


Essential trouble for simulation distribution on mobility
Essential trouble for simulation: simulation distribution on mobility

Example:

Experimantal spectrum

consist of:

rigid limit spectrum,

spectrum of slow rotation

spectrum of fast rotation

TEMPON absorbed on

Na-mordenite in presence of water vapor


Example of set of esr spectra temperature dependence
Example of set of ESR spectra: simulationTemperature dependence.

Experimental spectra:

100-150K

300-400K

150-300K

TEMPON in porous teflon AF-2400


Attempt of simulation using model of anisotropic brownian rotation
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
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
Results for whole temperature dependence: movesmovements of probes in polyvinyltrimethylsilane

We thank Prof. Kalman Hideg

and Dr.Tamas Kalai

for the gift of this substance.


Probe in liquid crystal 77k
Probe in liquid crystal 77K moves

Example of simulation of set of ESR spectra:Angular dependence of ESR spectrum.


Quantitative modelling of angular dependence gives the orientation distribution function
Quantitative modelling of movesangular dependence gives the orientation distribution function:

Distribution function is presented in molecular frame

A.Kh.Vorobiev, N.A.Chumakova,

J.Magn.Res. 2005, 175, No.1 pp.146



Orientation of probe molecule relative to liquid crystal are determined by quntitative simulation of spectra.


Dr. Vladimir Gurman determined by quntitative simulation of spectra.

Dr. Tatiana Klimenko

Natalia Chumakova

Daria Chernova

took part on presented work


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