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1
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Max von Laue (1879-1960) – pamięci uczonego w Międzynarodowym RokuKrystalografii 2014 i w 100-lecie przyznania mu Nagrody Nobla z fizyki

100%
Więckowski A.
Nauka
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2014
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issue 2
2
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Paramagnetic Centres in Coal Macerals

64%
Słowik G., Więckowski A.
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issue 3
507-510
EN
The electron paramagnetic resonance (EPR) study of coal macerals: exinite, vitrinite and inertinite separated from clarain of the Polish medium-rank coal with carbon content of 85.6 wt% C, were performed. Using the continuous microwave saturation technique (measurements at 223 K and 291 K), as a result of numerical analysis of recorded EPR spectra of exinite, vitrinite and inertinite, their multi-component structure was shown. The EPR spectra of exinite and vitrinite consist of three component lines: one Gaussian G and two Lorentzians: L1 and L3. The EPR spectra of inertinite consist of two narrow lines with Lorentzian line shape L2 and L3. Temperature measurements of studied coal macerals in the range 100-373 K were done. It was evidenced that, in group of paramagnetic centres responsible for Lorentzian L1 component line, paramagnetic centres with thermally excited triplet states (S = 1) exist. Existence of paramagnetic centres with thermally excited triplet states was not observed in inertinite.
3
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EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

64%
Wojtowicz W., Więckowski A.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
395-401
EN
This work is devoted to a study of the structural changes in a single crystal of ammonium nitrate, NH_4NO_3, doped with copper(II) cations by electron paramagnetic resonance. Ammonium nitrate crystallizes at atmospheric pressure in several polymorphic forms, phase VII → V → IV → III → II → I → melt, with transition temperatures of 103 K, 255 K, 305 K, 357 K, 398 K, and 443 K, respectively. The aim of our work was to study the temperature phase transition V → IV at about 255 K using electron paramagnetic resonance technique. The electron paramagnetic resonance spectra were performed using an X-band spectrometer with microwave frequency of 9.4 GHz and magnetic modulation of 100 kHz in the temperature range of 153-296 K. For a single crystal the angular dependence of the copper(II) electron paramagnetic resonance spectra was measured at 293 K and 168 K. The anisotropic behaviour measured at 293 K points to the existence of one kind of two equivalent copper(II) complexes with inverse g and A tensors. A second pair of equivalent complexes also with inverse g and A tensors was observed. The minimal values of g-factors correspond to the maximum values of A. The angular dependence taken at 168 K shows the existence of two types of non-equivalent copper complexes which differ in comparison with the complexes observed at room temperature. The temperature dependence of the intensities of hyperfine structure lines for all copper(II) complexes observed shows a phase transition V → IV occurring in the temperature range of 237-246 K with a hysteresis. One of the hyperfine structure lines of a copper(II) complex measured at low temperatures shows a superhyperfine structure with line intensities 1:2:3:2:1 originating from the interaction of the copper ^{63,65}Cu (I=3/2) nucleus with two ^{14}N (I = 1) nuclei of two ammonia, NH_3, ligand molecules.
4
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EPR Evidence for Thermally Excited Triplet States in Exinite, Vitrinite and Inertinite Separated from Bituminous Coal

51%
Słowik G., Wojtowicz W., Więckowski A.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
171-176
EN
In this work we have made an electron spin resonance (EPR) study of macerals obtained from the lithotype clarain separated from Polish medium-rank coal (85.6 wt.% C). For three macerals:~exinite, vitrinite, and inertinite, the temperature dependence of intensity of EPR spectra in the temperature range of 100-373 K was investigated. The experimentally obtained EPR spectra of macerals were fitted by curves of the derivatives of the Gaussian and Lorentzian functions. The best fitting was obtained, when the experimental EPR spectra were assumed to be a superposition of three lines, for exinite and vitrinite - a broad Gaussian (G), a broad Lorentzian (L1) and a narrow Lorentzian (L3) line, but for inertinite of two lines - a narrow Lorentzian (L2) and a narrow Lorentzian (L3) line. The computer-assisted fitting has shown that each individual component line has similar values of resonance field, but different linewidths and amplitudes. The temperature dependence of line intensity I of the broad Gaussian (G) and narrow Lorentzian (L2 and L3) lines fulfils the Curie law in the form I=C/T or IT=C, whereas the broad Lorentzian (L1) line does not fulfil the Curie law. In the last case the temperature dependence of the Lorentzian (L1) component was fitted by the relation I=C/T+B/[T(3+exp(J/kT))] or IT=C+B/[3+exp(J/kT))], valid for thermally excited triplet states (S=1). For exinite and vitrinite the curves presenting the temperature dependence of the product IT versus temperature T were resolved into two curves, one for paramagnetic centres in the doublet state (S=1/2), and the other for paramagnetic centres in the thermally excited triplet state (S=1).
5
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Multi-Component EPR Spectra of Coals with Different Carbon Content

51%
Pilawa B., Więckowski A., Pietrzak R., Wachowska H.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
403-407
EN
EPR spectra of lignite"Mequinenza" (Spain) (62.3 wt% C) and Polish orthocoking coal (87.8 wt% C) were compared. The spectra were superpositions of broad Gaussian, broad Lorentzian 1, and narrow Lorentzian 3 lines. Concentration of paramagnetic centers - mainly delocalizedπ electrons - responsible for narrow Lorentzian 3 lines increases with increase in carbon content in coal. Coal units with slow and fast spin-lattice relaxation processes exist in the two studied samples. Slow spin-lattice interactions occur in simple aromatic coal units with broad Gaussian and Lorentzian 1 lines. Fast spin-lattice relaxation processes are characteristic of large aromatic units with narrow Lorentzian 3 lines.
6
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EPR Study of Dealuminated HY Zeolite and Silica Containing Cu-Mn-Zn Spinels: The Effect of Support

45%
Decyk P., Więckowski A., Najder-Kozdrowska L., Bilkova I., Ziółek M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 1
38-44
EN
A mixture of antiferromagnetic Cu_{1.4}Mn_{1.6}O₄ and Cu_{0.5}Zn_{0.5}Mn₂O₄ or/and ZnMn₂O₄ spinels was prepared. Dealuminated HY zeolite and silica were doped by these Cu-Mn-Zn spinels. The materials were investigated by X-ray diffraction, the Fourier transform infrared spectroscopy and EPR spectroscopy. Additionally, all the samples were tested for their activity for isopropyl alcohol dehydration/dehydrogenation. Three EPR signals were observed for Cu-Mn-Zn/dealuminated HY and Cu-Mn-Zn/SiO₂ samples at 293 K. In contrast to the spectra recorded at 293 K, only one broad line attributed to Cu-Mn-Zn spinels was visible at 77 K. The EPR signal from pure Cu-Mn-Zn spinels consists only of a single broad line when recorded at 293 K, whereas at 77 K the line is narrower. For all samples subjected to evacuation at high vacuum up to 573 K, the Cu-Mn-Zn spinels were stable. The evacuation at 673 K resulted in a rapid lowering of the intensity of EPR spectrum.
7
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Paramagnetic Centres in Oxidised Coal

45%
Najder-Kozdrowska L., Samoilova R., Kappl R., Hüttermann J., Więckowski A.
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issue 3
475-479
EN
This paper comprises the results obtained by continuous wave (cw)/pulse electron paramagnetic resonance spectroscopy for oxidised coals. The values of EPR linewidths are different for samples of coal treated by different chemical agents. The asymmetric EPR line shape indicates to complex composition of paramagnetic centres in coal. In coal oxidised by HNO_3 big changes of linewidth with temperature were observed. For all samples the spin-lattice relaxation time T_1 was determined by pulse EPR method. The correlation between used chemical agents and the value of T_1 was established.
8
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Groups of Paramagnetic Centres in Reduced and Methylated Low Rank Coal

45%
Pilawa B., Wachowska H., Kozłowski M., Więckowski A., Najder-Kozdrowska L.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
264-267
EN
Low rank Illinois No. 6 coal was studied by electron paramagnetic resonance EPR spectroscopy. The parameters of EPR spectra (spectroscopic splitting factors g, linewidths ΔB_{pp}, concentrations of paramagnetic centres N) were measured for row and chemically treated coal (demineralized, reduced and methylated samples). The multi-component structure of experimental spectra of this coal was proved. Two groups of paramagnetic centres responsible for broad Lorentzian 1 and narrow Lorentzian 2 lines exist in studied samples. Paramagnetic centres connected with component lines revealed different behaviour during chemical treatments.
9
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Influence of Microwave Power on EPR Signal of Melanin Radical and Copper(II) Ions in DOPA-Melanin Complexes

45%
Najder-Kozdrowska L., Pilawa B., Więckowski A., Buszman E., Wrześniok D.
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EN
Electron paramagnetic resonance spectroscopy EPR was used for examination of microwave saturation in DOPA-melanin complexes with kanamycin and Cu(II) ions. The fast spin-lattice relaxation processes take place in system of paramagnetic metal ions. EPR signal of melanin radical saturated with growing of microwave power used during measurements. After adding Cu(II) ions a shortening of relaxation time is observed for EPR signal of melanin radical.
10
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Triplet States in DOPA-Melanin and in Its Complexes with Kanamycin and Copper Cu(II) Ions

39%
Najder-Kozdrowska L., Pilawa B., Buszman E., Więckowski A., Świątkowska L., Wrześniok D., Wojtowicz W.
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issue 4
613-618
EN
The mono- and biradical forms of DOPA-melanin (DOPA-eumelanin) were studied by EPR spectroscopy in 100-300 K temperature range. The existence of triplet states in DOPA-melanin was proved. The analysis of EPR spectra has shown that in DOPA-melanin and its complexes with kanamycin and Cu^{2+} ions, two kinds of paramagnetic centres exist. The first of them are in doublet ground state with spin S = 1/2 and they obey the Curie law. The paramagnetic centres of the second group are in thermally excited triplet state with spin S = 1 and in this case the Curie law is not fulfilled.
11
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EPR Characteristics of Activated Carbon for Hydrogen Production by the Thermo-Catalytic Decomposition of Methane

39%
Więckowski A., Najder-Kozdrowska L., Rechnia P., Malaika A., Krzyżyńska B., Kozłowski M.
Acta Physica Polonica A
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2016
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vol. 130
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issue 3
701-704
EN
The electron paramagnetic resonance (EPR) method was used to characterize samples of activated coal before and after reactions of the catalytic decomposition of methane and ethanol at temperatures of 1023 K (750°C), 1123 K (850°C) and 1223 K (950°C). The EPR parameters: spectroscopic splitting factor g, peak-to-peak linewidth ΔBₚₚ, and spin concentration c were measured. During the ethanol-assisted catalytic decomposition of methane carbon-located-spin radicals are partially transformed into oxygen-located-spin radicals.
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