Number Of Resonance Lines Research Articles

In Russian

The samples of silicas with covalently-immobilized aminodiphosphonic acid (SiO 2 –АDPA) have been characterized by the XPS and solid state 31 P NMR spectroscopy. The samples were synthesized via Kabachnik-Fields reaction from aminopropyl silica gel, H 3 PO 3 and formaldehyde, and have different concentrations (0.33–1.67 mmol/m 2 ) of grafted groups and different yield (59–86%). It is demonstrated that chemical shift of the lines and number of resonance lines in the 31 P NMR spectra of SiO 2 –АDPA depends on both the concentration of bonded groups and the yield. This difference was interpreted as a result of heterogeneity in the local environment of SiO 2 –АDPA surface.

EPR, optical and superposition model study of Mn2+ doped L+ glutamic acid

Electron paramagnetic resonance (EPR) study of Mn2+ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from 6A1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter–electronic repulsion parameters B = 869 cm−1, C = 2080 cm−1 and cubic crystal field splitting parameter Dq = 730 cm−1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.

133Cs Nuclear Magnetic Resonance Relaxation Study of the Phase Transition of Cs2MnCl4·2H2O Single Crystals

The structural phase transition of single crystals was investigated by determining the spin-lattice relaxation time . The number of resonance lines in the spectrum changes from seven to one near 375 K, which means that above 375 K the Cs sites are symmetric. Further, the of the nucleus undergoes a significant change near 375 K, which coincides with the change in the splitting of the resonance lines. The change in near is related to the loss of , and means that the forms of the octahedra of water molecules surrounding are disrupted.

Ferromagnetic ordering of iron impurities in the valence-fluctuating semiconductor SmB6

The electron paramagnetic resonance (EPR) of the valence-fluctuating semiconductor SmB6 doped by 1 at % Fe is studied. The EPR measurements are performed on a SmB6 single crystal in a temperature range of 1.6–300.0 K. A number of resonance lines whose g factors indicate the presence of iron ions in the Fe0, Fe+, Fe2+, and Fe3+ states have been detected. The iron ions are ferromagnetically ordered below a Curie temperature T = 100 K, and this ordering can be caused by the exchange interaction of impurity ions due to matrix polarization (a similar mechanism is observed in PdFe alloys). This exchange interaction is estimated to be significantly higher than that in PdFe; this fact can result from a very high density of states in the narrow f band, which is characteristic of a valence-fluctuating material.

EPR and optical study of Mn2+-doped bis(l-Asparaginato)Zn(II)

Abstract EPR and optical studies of single crystals of Mn2+: bis( l - A sparaginato)Zn(II) are reported. The spin-Hamiltonian parameters are determined employing the positions of a large number of resonance lines for various orientations of the external magnetic field. The best-fit zero-field parameters to the observed EPR spectra are obtained as, D=(228±2)×10−4 cm−1, E=(58±2)×10−4 cm−1 and a=(−12±1)×10−4 cm−1,whereas g=2.0002±0.0002, A = ( 74 ± 2 ) × 1 0 - 4 cm - 1 , and B = ( 62 ± 2 ) × 1 0 - 4 cm - 1 . From the optical absorption study, the lattice distortion is suggested. The electron repulsion parameters (B and C) and crystal field parameters (Dq and α) evaluated from the fitting of observed optical spectra are: B=858 cm−1, C=2620 cm−1, Dq=950 cm−1, and α=76 cm−1.

Ferromagnetic ordering of iron impurities in the mixed-valence semiconductorSmB6

Electron spin resonance (ESR) was studied in the mixed-valence (MV) semiconductor $\mathrm{Sm}{\mathrm{B}}_{6}$ doped with $1\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$ of Fe. The ESR measurements were performed on a single crystal of $\mathrm{Sm}{\mathrm{B}}_{6}$ in the temperature range $1.6--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. A number of resonance lines were found with $g$ factors indicating the presence of iron in ${\mathrm{Fe}}^{0}$, ${\mathrm{Fe}}^{+}$, ${\mathrm{Fe}}^{2+}$, and ${\mathrm{Fe}}^{3+}$ states. Ferromagnetic ordering of iron ions is observed below the Curie point at $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which can be attributed to indirect exchange of impurity ions via polarization of the matrix (a mechanism similar to that found in PdFe alloys). However, the estimate of the intensity of this indirect exchange demonstrates a large enhancement compared to its value in PdFe, caused by the extraordinarily high density of states in a narrow $f$ band, characteristic of a material with fluctuating valence.

NMR study of the order–disorder phase transitions of KHCO 3 and KDCO 3 single crystals

KHCO 3 and its deuterated analogue KDCO 3 are typical materials that undergo order–disorder phase transitions at 318 and 353 K, respectively. The spin–lattice relaxation times, T 1, spin–spin relaxation times, T 2, and the number of resonance lines for the 1H, 2D, and 39K nuclei of these crystals were investigated using NMR spectrometer. These materials are known to exhibit anomalous decreases in T 1 near T C, which have been attributed to a structural phase transition. Additionally, changes in the symmetry of the (HCO 3) 2 2− (or (DCO 3) 2 2−) dimers in these materials are associated with large changes in T 1, T 2, and the number of resonance lines. Here we found that the resonance lines for 1H, 2D, and 39K nuclei decrease in number as the temperature is increased up to T C, indicating that the orientations of the (HCO 3) 2 2− (or (DCO 3) 2 2−) dimers and the environments of the K ions change at T C. Moreover, based on number of resonance lines, the results further indicate that the (HCO 3) 2 2− (or (DCO 3) 2 2−) dimers reorientate to approximately parallel to the directions of the hydrogen bonds (or deuteron bonds) and the direction of the a-axis. The transitions at 318 and 345 K of the two crystals are of the order–disorder type. The present results therefore indicate that the orientations of the (HCO 3) 2 2− and (DCO 3) 2 2− dimers and the environment of the K ion play a significant role in these phase transitions.

The Investigation of Molecular Dynamics in Pyridinium Perchlorate Single Crystal by CW-EPR Spectroscopy Combined with Computer Resolution Enhancement Method

This paper illustrates the application of CW-EPR combined with the Computer Resolution Enhancement Method (CREM) to the investigation of the phase transitions and molecular dynamics of radicals in pyridinium perchlorate single crystals. The CREM method is based on the Fourier transform, convolution and deconvolution functions and permits determination of the fundamental parameters of the spectra: the number of resonance lines, their positions, relative ratios of intensities and core width parameter. Thanks to the use of the simulation procedure, we are able to determine the widths of individual spectral lines. An example illustrating the advantages following from the application of the CREM method in the analysis of complex CW-EPR spectra of organic radicals is the possibility of determination of basic parameters, such as the spectroscopic splitting factor, hyperfine coupling constants and widths of individual spectral lines in EPR spectra recorded in wide range of temperatures. Phase transitions and changes in molecular dynamics of radicals may imply changes in their electron structure, which may affect the above-mentioned parameters of CW-EPR spectra.

A Fast Variant of 1H Spectroscopic U-FLARE Imaging Using Adjusted Chemical Shift Phase Encoding

So far, fast spectroscopic imaging (SI) using the U-FLARE sequence has provided metabolic maps indirectly via Fourier transformation (FT) along the chemical shift (CS) dimension and subsequent peak integration. However, a large number of CS encoding steps Nω is needed to cover the spectral bandwidth and to achieve sufficient spectral resolution for peak integration even if the number of resonance lines is small compared to Nω and even if only metabolic images are of interest and not the spectra in each voxel. Other reconstruction algorithms require extensive prior knowledge, starting values, and/or model functions. An adjusted CS phase encoding scheme (APE) can be used to overcome these drawbacks. It incorporates prior knowledge only about the resonance frequencies present in the sample. Thus, Nω can be reduced by a factor of 4 for many 1H in vivo studies while no spectra have to be reconstructed, and no additional user interaction, prior knowledge, starting values, or model function are required. Phantom measurements and in vivo experiments on rat brain have been performed at 4.7 T to test the feasibility of the method for proton SI.

Computer enhancement of CW-EPR experimental spectra resolution as a new method in investigation of molecular dynamics in pyridinium tetrafluoroborate

The present paper reports an application of the computer method for enhancing resolution of complex CW-EPR spectra. The computer resolution enhancement method (CREM) is based on the Fourier transform, convolution and deconvolution of functions and permits determination of the fundamental parameters of the spectra: the number of resonance lines, their positions, core width parameter, and relative ratios of intensities. Thanks to the use of a simulation procedure performed with the earlier determined parameters of the spectra, we were able to find the temperature changes of the widths of individual spectral lines. An example illustrating the advantages of the CREM is the possibility of investigation of molecular dynamics and phase transitions by the CREM-aided CW-EPR. Dynamics of the radical in a complex of pyridine with tetrafluoroboric acid is reflected in changes in the hyperfine structure, core width parameter and width of individual lines in the spectrum. These changes are detectable for the complex in both powdered and single-crystal form.

EPR measurements on K3Co(CN)6 doped with K3Fe(CN)6: a determination of the polytype crystal structure of K3Co(CN)6

In this paper it is shown that with EPR the polytype structure of K3Co(CN)6 single crystals doped with Fe(CN)3- 6, can be determined easily. The number of resonance lines for an arbitrary orientation of the magnetic field is indicative of the type of crystal studied. This is substantiated by the known crystallographic data concerning K3Co(CN)6.

Circumstellar clouds derived from ultraviolet stellar spectra

It is shown that the observed variety in macrostructures of continuous spectra in the ultraviolet (2000–3000 A) of hot stars is a result of the presence of circumstellar clouds around such stars. A method for calculations of synthetic spectra, originating as a result of passage of central star photospheric radiation through its own circumstellar cloud, is developed. It introduces a new idea of spectral class for circumstellar cloud, and a recommended method for its determination depending from the spectral class of central star and cloud's parameters (Figure 2). The results of calculations of synthetic spectra for the four combinations of system ‘star+cloud’ are presented (Figures 7-10). The strongest influence of circumstellar cloud in ultraviolet is discovered on A-class stars (Figure 13). Graphic relations are introduced for determination of cloud power by observed parameters of synthetic spectra (Figures 14 and 15). It establishes an important fact for an understanding of the nature of circumstellar clouds and processes occurring in them, according to which the selective absorption in such clouds stimulatesresonance lines only, the largest number of which lies in the ultraviolet in the region of 2100–2600 A (Figure 1). An absence of visible signs of the effect of circumstellar clouds on continuous spectra of stars in visual region can be explained by a very small number of resonance lines in this region. Lastly, the possibility of determination of physical and geometric parameters of circumstellar clouds from stellar continuous spectra in the ultraviolet is analysed.

ChemInform Abstract: NUCLEAR QUADRUPOLE RESONANCES OF PHOSPHORUS IODIDES AND SOME PHOSPHORUS TRIHALIDE‐BORON TRIHALIDE COMPLEXES

Nuclear quadrupole resonance (NQR) frequencies due to 79Br and 127I are examined in phosphorus iodides, PI3 and P2I4, and the complexes PBr3·BBr3, PBr3·BI3, and PI3·BBr3. The quadrupole coupling constants and asymmetry parameters are also derived for 127I in PI3, P2I4, and PBr3·BI3. The resonance lines of PI3 fade out above 257 K, at which temperature a structural phase transition is suggested. The number of resonance lines in P2I4 shows that the molecular symmetry of P2I4 is \bar1 instead of 2/m in its crystal. The similarity of the resonance patterns of the three complexes indicates that they are isomorphous with one another. The electronic structures of the halogens in the compounds mentioned above have been discussed by using the Townes-Dailey theory. On complexing, the electric charge of the halogen atoms in the donor PX3 decreases due to the polarization of pσ bonds, whereas that of the halogen atoms in the acceptor BY3 increases owing to the backdonation through pπ bonds.

Nuclear Quadrupole Resonances of Phosphorus Iodides and Some Phosphorus Trihalide–Boron Trihalide Complexes

Abstract Nuclear quadrupole resonance (NQR) frequencies due to 79Br and 127I are examined in phosphorus iodides, PI3 and P2I4, and the complexes PBr3·BBr3, PBr3·BI3, and PI3·BBr3. The quadrupole coupling constants and asymmetry parameters are also derived for 127I in PI3, P2I4, and PBr3·BI3. The resonance lines of PI3 fade out above 257 K, at which temperature a structural phase transition is suggested. The number of resonance lines in P2I4 shows that the molecular symmetry of P2I4 is \bar1 instead of 2/m in its crystal. The similarity of the resonance patterns of the three complexes indicates that they are isomorphous with one another. The electronic structures of the halogens in the compounds mentioned above have been discussed by using the Townes-Dailey theory. On complexing, the electric charge of the halogen atoms in the donor PX3 decreases due to the polarization of pσ bonds, whereas that of the halogen atoms in the acceptor BY3 increases owing to the backdonation through pπ bonds.

Line Absorption Studies of the Interstellar Gas Near 1015 Hz

The Copernicus satellite now opens up the ultraviolet region for inspection, and the number of resonance lines which may be studied has increased from 6, seen in the visible, to more than 30. The distribution and properties of an important constituent of the interstellar gas, molecular hydrogen, can be studied in detail using this instrument. A more comprehensive picture may now be developed for element depletion factors, electron densities, and sources of ionization (UV photons, low energy cosmic and X-rays).

Nuclear quadrupole resonance of halogens in tetrahaloaurates(III)

The nuclear quadrupole resonance of halogens in a variety of anhydrous and hydrated tetrahaloaurates(III) was observed between 77 and 400°K. From the number of resonance lines, the number of different kinds of crystallographically nonequivalent halogen atoms was determined. The ionic character of AuCl and AuBr bonds is estimated as 41% and 34%, respectively. The central gold atom in the tetracoordinated complex ion carries a fraction of protonic charge (0.64ϵ in [AuCI 4] − and 0.36ϵ in [AuBr 4] −, respectively). The positive temperature coefficient of resonance frequencies observed for some tetrahaloaurates(III) is attributable to hydrogen bond formation. The anomalous temperature dependence of bromine resonance frequency of cesium tetrabromoaurate(III) is presumed to be due to the torsional oscillation of tetrabromoaurate(III) ions in crystals involving a considerable anharmonicity.

Phase transitions in some hexahalostannates(IV) as revealed by the pure quadrupole resonance of halogens

The quadrupole resonance of halogens in potassium hexachlorostannate(IV), potassium hexabromostannate(IV), ammonium hexachlorostannate(IV), ammonium( d 4) hexachlorostannate(IV), and ammonium hexabromostannate(IV) was observed over a wide range of temperature, and transition points were located. The nature of the phase transitions is discussed from the number of resonance lines, the continuity or discontinuity of resonance frequencies at the transition points, and the temperature coefficient of resonance frequencies.