A computer algorithm is presented for the simulation of the effect of molecular tumbling on ESR spectra, and is applied to simulation of the conventional ESR signal (the absorption signal detected at the first harmonic of the modulation frequency and in-phase with the modulation frequency, in the limit of low microwave and modulation power) of axially symmetric 14N-nitroxide spin labels. The algorithm is extremely fast and is economical in terms of computer memory requirements. 相似文献
A fast algorithm for the numerical solution of the stochastic Liouville equation is presented. Applications to simulations of slow-motion ESR, ELDOR and saturation-transfer ESR spectra are discussed. 相似文献
EPR imaging was applied to the study of several important processes in polymers and materials. The solvent diffusion and induced swelling was visualized in the water/DMF or toluene/DMF interactions with polycarbonate or polystyrene molded rods. The cross-sectional images revealed non-homogeneous solute/solvent diffusion, rod expansion and crack development. The ESR lineshapes in all cases above confirmed that the nitroxide imaging agent did not interact significantly with the polymer matrix; thus the paramagnetic distribution reflected bulk solvent distribution quite well. The diffusion of an electrolyte buffer (Krebs) solution containing a nitroxide spin probe was followed in a cross-sectional image of a polyacrylamide gel rod. A one-dimensional radial diffusion constant was calculated for the solvent piperidinol nitroxide spin probe, TEMPOL. Lastly, solid coal rods were monitored during mild pyrolysis at 150°C in air. Here the naturally occurring organic radical composition was imaged. Even with the increase in total ESR signal and subsequent decline to ca. the initial levels, the coal rod cross-section was essentially homogeneous in paramagnetic centers throughout the heating process. All of the imaging above utilized a homemade L-band, flat loop surface coil spectrometer. 相似文献
We have undertaken Ar plasma irradiation on poly(ethylene naphthalate) (PEN) powder, and the radicals formed were studied
by electron spin resonance (ESR). The room temperature ESR spectrum of plasma-irradiated PEN shows a five-line spectrum separated
with nonbinomial intensity distribution, indicating that the spectrum is an outline of multicomponent spectra. The systematic
computer simulation of the observed ESR spectra disclosed that the spectra consist of two types of radicals in structural
term: the major radicals formed were assigned to dihydronaphthalenyl-type radicals generated by a nearly random addition of
a hydrogen atom to the naphthalene ring, and immobilized dangling bond sites at the surface crosslinked moiety. 相似文献
A method for determination of the orientation distribution function of anisotropic paramagnetic species from the angular dependence of the ESR spectra based on simulation of the spectra was developed. The orientation distribution function is represented as a sum of orthonormal functions. The weight coefficients are determined by minimizing the deviations of the theoretical spectra from experimental ones. The method was numerically tested. The method is relatively insensitive to the presence of noise and foreign ESR signals not related to the sample orientation in the magnetic field.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2595–2601, December, 2004. 相似文献
The anion radical of the fully aromatic di-N-oxide system of azobispyridine N-oxide was prepared and studied by ESR. Utilising computer simulation and CNDO computation the ESR spectrum was interpreted as follows: Using appropriate equations the spin densities were calculated at Ths semi-quinoidal nature of the radical suggests a possible use as a spin label. 相似文献
Electron spin resonance spectra have been measured under uniform conditions for a series of trimethylsilyl-substituted benzene anion radicals. These ESR results have been used to derive a general set of Hückel molecular orbital parameters by treating the organosilyl substituent as a pseudo-heteroatom. ESR data for radical anions of organosilyl-substituted benzenes, biphenyls and naphthalenes are reproduced accurately by MO calculations employing hSi = –2.0 and kCSi = 0.7. For these series of compounds, the silicon-methyl proton ESR splittings, while not related to the π electron density on silicon alone or to the density on the aromatic carbon to which silicon is bonded, may be related to a combination of the π spin densities by a semiempirical relation: 相似文献
The solution ESR spectra of Mn(II) bound to ATP have been analyzed at three microwave frequencies. The liquid-type relaxation process induced by rapid fluctuations of the crystal-field symmetry does not account for the frequency dependence of the linewidth. The ESR lineshapes are better explained in terms of a static distribution of crystalfield sites which induces field dependent inhomogeneous broadening. 相似文献
