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Numerical simulation of ESR spectra of nitrixides as a method of investigation. Andrey Kh. Vorobiev Moscow State Univers

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. Vorobiev Moscow State Univers

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  1. Numerical simulation of ESR spectra of nitrixides as a method of investigation.Andrey Kh. VorobievMoscow State University

  2. Typical result of simulation of single ESR spectrum: qualitative accordance; small deviations from experiment. • SiON(O) CD3 Rus.Chem Bull.V.50, No.12, p.2384

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

  4. Proposed thesis: 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).

  5. Anisotropic line width is often 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

  6. Distribution on magnetic parameters prevent to quantitative simulation Example: TEMPON in polystyrene 110K Admixture of species with other magnetic parameters gives marked component.

  7. Essential trouble for 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

  8. Example of set of ESR spectra:Temperature dependence. Experimental spectra: 100-150K 300-400K 150-300K TEMPON in porous teflon AF-2400

  9. Attempt of simulation using model of anisotropic Brownian rotation: Deviations are more then experimental errors! High temperature part of dependence

  10. 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

  11. Quasilibration: avereging on frequency, limited on amplitude moves. Moves around three axes should be taken into account in general.

  12. Results for whole temperature dependence:movements of probes in polyvinyltrimethylsilane We thank Prof. Kalman Hideg and Dr.Tamas Kalai for the gift of this substance.

  13. Probe in liquid crystal 77K Example of simulation of set of ESR spectra:Angular dependence of ESR spectrum.

  14. Quantitative modelling of angular 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

  15. Relaxation of orientation distribution function at the annealing 77К 195К 236К 226К

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

  17. Dr. Vladimir Gurman Dr. Tatiana Klimenko Natalia Chumakova Daria Chernova took part on presented work

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