ESR spectra simulation

Fig. 1.23. ESR spectra simulation for (a) 9.5 GHz and (b) 95 GHz frequency ranges. Parameters of g-tensors and line width are identical...

Fig. 6.3 (a) Experimental ESR spectra of NO adsorbed on Na-LTA zeolite at 10 K observed at X-, Q- and VE-band microwave (MW) resonance frequencies. NO was adsorbed onto activated Na-LTA samples at room temperature with a gas pressure corresponding to approximately 10 molecules per unit cell, (b) ESR spectra simulated using an identical set of the A and g ESR parameters in Table 6.1. The figure is adapted from [28] with permission from the Royal Society of Chemistry... 

Key words EPR ESR ranked system molecule ordering ordered films copper phthalocyanine copper dipivaloilmethanate ESR spectra simulation ... 

PMR and DMR lineshape analysis, ESR spectra simulation, x-ray scattering, IR dichroism and UV dichroism. ... 

Figure 1. ESR spectra at some temperatures of X-irradiated polycrystalline frozen solutions (c a 1 mol%) of C5H5 and CgH5D, respectively, a) at 15 K. b) simulated spectrum by using the parameters shown in Table 4. c) 05 150 " " at 30 K in CFCI3. d) simulation using hyperfme coupling data shown in Table 4 for a mixture of component 1 component 2 of C6H5D . The ratio 1 2 = 0.38 0.62 obtained from the component analysis of Figure 2 was employed.

Figure 2. Component analysis of an X-irradiated polycrystalline frozen solution (c a 1 mol%) of C6H5D in CFCI3. a) simulated components 1 (dashed) and 2 (solid) using hyperfine coupling data from ENDOR (Table 4). b) experimental (solid) and fitted (dashed) ESR spectra of CgH5D...

Hyde, J. S. and W. K. Subczynski. 1984. Simulation of ESR spectra of the oxygen-sensitive spin-label probe CTPO. J. Magn. Reson. 56 125-130. 

Figure 6 Simulated ESR spectra of nitroxides (a) in the absence of magnetic field gradient (b) ID image for a homogenous radical distribution (in the presence of a gradient) and (c) ID image for radicals present only in thin layers near both surfaces of the plaque (in the presence of a gradient).

Figure 2.8 ESR spectra resulting from the reduction of PhCN (bottom) and />-F-PhCN (top). The top spectrum is identical to that of the 4,4 -dicyanobiphenyl anion radical. (Spectra were simulated using hyperfine couplings with permission from ref. 16, copyright (1963) American Chemical Society.)...

Figure 2.10 ESR spectra of o-, m-, and p-xylene radical anions (see text for assignment of spectra). Spectrum (a) was simulated with permission using hyperfine parameters from Ref. 17b, copyright (1964) American Institute of Physics spectra (b) and (c) were simulated with permission using hyperfine parameters from ref. 17a, copyright (1961) Taylor and Francis (www.tandk. co.uk).

Figure 4.12 [E] Computer-simulated ESR spectra for a hypothetical low-spin Mn(n) radical with g = (2.100, 2.050, 2.000), AMn = (150, 25, 25) x 10-4 cm-1, for various values of / , the Euler angle between the g-matrix and hyper-...

With ESR spectroscopy, open-shell species can be observed and characterized as long as their total spin differs from zero. With variable-temperature ESR spectroscopy, it is possible to deduce whether the observed multiplicity is a thermally populated excited state or is the ground state [69]. From such experiments, the T-S splittings of a variety of biscarbene and bisnitrenes have been determined. ESR spectroscopy is very sensitive to paramagnetic species, and because it does not see any singlet impurities or by-products, it is relatively easy to pick out the desired signals. At the same time, analysis of ESR spectra is not trivial and special simulations are required for their interpretation. 

Figure 6 (a) ESR spectrum of MeAcrPh in deaerated MeCN at 298 K and the computer simulation spectrum, (b) Plots of versus [MeAcrPh ] for the ESR spectra of... 

The results of the simulations are shown in Figures 1 and 2, superimposed on the experimental results. The agreement between calculated and experimental spectra is very good. Numerous simulations were performed in order to assess the effect of the various parameters. The results indicate that the simulated spectra are very sensitive to the choice of the distribution parameters and to the values of the residual widths AH and AH . Given the limited possibilities of measuring ESR spectra at S-band, we believe that computer simulations are a viable alternative. We also feel that the error margin in the parameters deduced by computer simulation can be decreased if ESR spectra of isotopically enriched Cu are measured and Simulated 4. 

Figure 11 Observed (—) and simulated (—) ESR spectra of permethyloligosilane radical cations at 77 K in y-irradiated freon matrices. The simulations were carried out under the assumption that an unpaired electron is delocalized over the entire Si-Si chain.

Frozen-solution ESR spectra of Tc2G in mixed aqueous hydrochloric acid and ethanol provided data consistent with equal coupling of the unpaired electron to both technetium nuclei (101). IsotopicaUy pure "Tc (/ = 9/2) in 99Tc2Cl leads to a large number of lines in the X-band spectrum owing to second-order effects, in addition to the hyperfine lines presence for this dimeric axially symmetric system. The Q-band spectrum obtained at 77°K with a microwave frequency of 35.56 GHz exhibited fewer lines, and computer-simulated spectra were generated to correspond to the experimental spectrum withgit = 1.912, gi = 2.096, An = 166 x 10 4 cm"1, IAL = 67.2 x 10 4 cm 1, and gav = 2.035. 

Marcus has introduced a model for, S N 2 reactions of the ET type based on two interacting states which takes into account the relevant bond energies, standard electrode potentials, solvent contributions, and steric effects.87 The rate constant for intramolecular electron transfer between reduced and oxidized hydrazine units in the radical cation of the tetraazahexacyclotetradecane derivative (43) and its analogues has been determined by simulation of then variable temperature ESR spectra.88 The same researchers also reported then studies of the SET processes of other polycyclic dihydrazine systems.89,90... 

Since identical ESR spectra were obtained on U.V. irradiation at liquid nitrogen temperature of PVC, copolymer of vinyl chloride with vinyl bromide and 3-chloropentane it is concluded that this radical is the "Radical I." This radical may play an important role in PVC degradation. To further firmly establish the identity of this radical, theoretical analysis of "Radical I" and computer simulations of ESR spectrum were performed. The polymer radical ESR spectra are very sensitive to the conformation of the chain. The characteristic chain conformation of vinyl syndiotactic sequences in solution has been shown (23) to consist chiefly of trans-trans groups, separated by gauche units . .. (TT)X (GG)i (TT)y (GG)y (TT)Z. .. 

Figures 1.23a and b illustrate computer simulated ESR spectra of positive polaron P+ and C "0 signals in two frequency ranges, (a) 9.5 GHz and (b) 95 GHz with identical components of the -tensors, line width and amplitudes. The signals that overlap at 9.5 GHz can be clearly separated at 95 GHz, and coincide with the experimental ones in one important aspect the (/-anisotropy can be clearly resolved.

Table 3.40 Simulated splitting constants (mT) in ESR spectra of 5-nitro-2,1,3-benzothiadiazole RA (DMF)a ...

In order to simulate the ESR spectra of these radicals twist had to be allowed for in the bonds to the phenyl groups. For 149, the 2(5)-phenyl twist is estimated at ca. 20° and the 3(4)-phenyl twist at ca. 60° for 150, coplanarity of the 2-phenyl and imidazole rings is indicated while the 4(5)-phenyl groups are twisted 30° from coplanar.492 Concordant results have been obtained for tetraarylpyrrolyl radicals by Broser et al. who studied the variation of the 0-factor with substituents.493... 

Many research groups have observed TR ESR spectra under photolysis of DAR, IRG651, TPO, and BAPO (Scheme 12.1) and of other Type 1 Pis. Analysis of ESR spectra of the primary radicals formed and their spin adducts allows determination of radical structure. Computer simulation with user-friendly software was used to elucidate the radical structure. 

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