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EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

100%
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.
2
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EPR Evidence for Thermally Excited Triplet States in Exinite, Vitrinite and Inertinite Separated from Bituminous Coal

81%
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).
3
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EPR Spectroscopy of the Mn^{2+} and Cu^{2+} Centres in Lithium and Potassium-Lithium Tetraborate Glasses

71%
Padlyak B., Wojtowicz W., Adamiv V., Burak Y., Teslyuk I.
Acta Physica Polonica A
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2010
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vol. 117
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issue 1
122-125
EN
The electron paramagnetic resonance spectra of the glasses with Li_{2}B_{4}O_{7} and KLiB_{4}O_{7} compositions doped with Mn and Cu were investigated. On the basis of obtained EPR spectra analysis it was shown that the Mn and Cu impurities are incorporated into the glass network as Mn^{2+} (^{6}S_{5/2}, 3d^{5}) and Cu^{2+} (^{2}D_{5/2}, 3d^{9}) ions. The Mn^{2+} EPR spectra in the glasses with Li_{2}B_{4}O_{7} and KLiB_{4}O_{7} compositions are characterised by the following parameters, measured at T = 300 K: isotropic g-factor (g_{iso} = 2.00 ± 0.05), isotropic hyperfine constant (A_{iso} = (8.65 ± 0.05) mT) and peak-to-peak linewidth of hyperfine components ΔB_{pp} = (3.50 ± 0.05) mT. The Cu^{2+} EPR spectra in the glasses with Li_{2}B_{4}O_{7} and KLiB_{4}O_{7} compositions, registered at T = 300 K are characterised by the same g-values (g_∥ = 2.34 ± 0.05, g_⊥ = 2.06 ± 0.05) and peak-to-peak line width of hyperfine components (ΔB_{pp}^{∥} = (5.11 ± 0.05) mT, ΔB_{pp}^{⊥} = (1.80 ± 0.05) mT), whereas anisotropic hyperfine constants show some differences (A_{∥} = (14.28 ± 0.05) mT, A_{⊥} = (2.34 ± 0.05) mT for glass with Li_{2}B_{4}O_{7} composition and A_{∥} = (14.21 ± 0.05) mT, A_{⊥} = (2.55 ± 0.05) mT for glass with KLiB_{4}O_{7} composition). The possible local structure of the Mn^{2+} and Cu^{2+} centres in the lithium and potassium-lithium tetraborate glass network has been considered.
4
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Triplet States in DOPA-Melanin and in Its Complexes with Kanamycin and Copper Cu(II) Ions

61%
Najder-Kozdrowska L., Pilawa B., Buszman E., Więckowski A., Świątkowska L., Wrześniok D., Wojtowicz W.
Acta Physica Polonica A
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2010
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vol. 118
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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.
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