The structural properties of crude oils and asphaltenes, especially related to the dynamics of their aggregation, have been investigated by different experimental and theoretical methods during the last few decades. However, there are only a few works devoted to study the dynamics of asphaltenes in a native hydrocarbon environment. In this report, we illustrate a possibility to use electron paramagnetic resonance (EPR) spectra of vanadyl porphyrins in asphaltenes for the qualitative and quantitative analysis of their rotational mobility in the crude oil samples. On the basis of the simulation of the EPR spectra, a simple semi-empirical parameter sensitive to the transition between motional regimes is proposed. This mobility parameter can be potentially useful for the prediction and analysis of the thermal influence on heavy oil reservoirs during hydrocarbon production. It is found that the rotational correlation time of the complexes in heavy oil samples changes discontinuously with the temperature. The observed jump could be attributed to a disaggregation of supramolecular complexes of asphaltenes in the close vicinity of a phase transition.

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A combined magnetic resonance, photoluminescence, photoconductivity, and Raman scattering study of ZnO is presented. Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy identify substitutional Al as a binding core of a shallow, effective-mass-like donor in ZnO. Based on the correlation between the EPR and photoluminescence data it is shown that recombination of an exciton bound to Al gives rise to the 3360.7 meV photoluminescence line (I 6 ). A 1s ! 2p donor transition at 316 cm À1 is detected in photoconductivity and Raman spectra.

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Structural characterization of asphaltenes in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. Various analytical tools and approaches are used for that. We present the results of our study of asphaltene fractions A1 and A2 with the predominantly “island” type and “archipelago” type asphaltene molecules by conventional and pulsed electron paramagnetic resonance (EPR) at X-band (9 GHz) and W-band (95 GHz) with aim to expand the abilities of EPR technique for asphaltene characterization. Shift to the higher frequencies allows to separate spectrally the contributions from paramagnetic complexes of different origin, define the EPR parameters more accurately comparing to the conventional X-band EPR. Application of pulsed techniques allows (at least partially) to separate the radicals in time domain. Features of the obtained spectra are described. Electronic relaxation times are found to be different for stable “free” radical for A1 and A2 fractions. We suggest that the obtained results can be used for investigation of various petroleum systems.