A Computer Program to Help Resolution of Complex and Poorly Resolved Cu2+ and VO2+ Ions Doped Single Crystals Electron Paramagnetic Resonance Spectra

Complex and poorly resolved Cu²⁺ and VO²⁺ doped single-crystal electron paramagnetic resonance (EPR) spectra are some of the serious problems that exist in this area. In order to help the resolution of this sort of spectra, and for easily resolvable spectra as well, a versatile computer program known as EPR RESolution, or EPRES, is presented. All detectable line positions in the single-crystal spectra taken in three mutually perpendicular planes are given as input. The program plots these line positions. The user then manually determines the lines by selecting the true data points on the plot and fitting them to a well-known variation function. If selection is not suitable, the process is canceled and renewed. By this process, as many resolvable lines as in the spectra can be resolved and determined. The user then groups the resolved lines according to the paramagnetic center to which they belong. This includes the attribution of correct nuclear spin I and M _I to correct lines. After this step, hyperfine and g tensor elements can be found, constructed, and diagonalized.

[Supplemental materials are available for this article. Go to the publisher's online edition of Spectroscopy Letters for the following free supplemental resource: a copy of the EPRES computer program.]     

宝石级锆石中Gd3+的电子顺磁共振

本文测量了含有微量Gd³⁺杂质并具有四角对称结构的天然锆石单晶的电子顺磁共振谱。用最小二乘法拟合技术严格地计算了精细结构参数。Gd的奇数同位素的超精细结构清晰可辨,并给出了超精细耦合常数的一级近似值。 关键词：     

The Current State of Measuring Bimolecular Spin Exchange Rates by the EPR Spectral Manifestations of the Exchange and Dipole–Dipole Interactions in Dilute Solutions of Nitroxide Free Radicals with Proton Hyperfine Structure

Experimental studies of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol) in 60 wt% aqueous glycerol were carried out for temperatures from 273 to 340 K. Selective isotope substitution allowed comparisons between the experimental spectral manifestations of spin exchange and dipole–dipole interactions for protonated, deuterated, ¹⁵N, and ¹⁴N Tempol. Theoretical spectra were computed from a rigorous theory specifically formulated to include proton hyperfine interactions over a wide range of spin exchange and dipole–dipole interactions to compare with the experimental data. For spin exchange and dipole–dipole interactions small compared with the proton hyperfine coupling constant, spectra were calculated with perturbation theory to gain insight into the behavior of individual proton lines. The theoretical and experimental spectra were analyzed by least-squares fitting to Voigt shapes or by a new two-point method. For most accessible experimental designs, the comparisons are rather good; however, for an experiment constrained to low concentrations and high viscosities, the methods are less accurate.     

Electron paramagnetic resonance study of Cu-Co interactions in Ba2Co(HCOO)64 H2O

Electron paramagnetic resonance studies of Cu²⁺ doped in single crystals of dibarium cobalt formate tetrahydrate are carried out. Unlike in other cobalt salts, resolved hyperfine spectra are observed at room temperature itself. At 77K, the hyperfine linewidth shows an angular and nuclear spin dependence. Further, the linewidth increases as the temperature is lowered. The various possibilities of Cu-Co couplings like spin-flip and cross relaxation etc. are discussed. The spin-Hamiltonian parameters change conspicuously as the temperature is lowered which is ascribed to a vibrational mixing of the electronic levels in the ground state of Cu²⁺.     

Methodology of interfacial regions in FeMCuB‐type nanocrystals

A fitting model based on the use of two independent blocks resulting from distributions of hyperfine fields and one sextuplet of Lorentzian lines is introduced to simulate Mössbauer spectra of FeMCuB‐type nanocrystals. It is discussed for the spectra of M = Mo, Nb, and Ti alloys in the first stage of crystallization. One distribution is ascribed to the amorphous residual matrix, while the other is attributed to Fe atoms located in the interface zone. The sextuplet of Lorentzian lines identifies α-Fe crystalline phase. Three‐dimensional mappings of hyperfine field distributions and models of structural arrangement and topography of hyperfine interactions are briefly reported.     

High resolution C nuclear magnetic resonance spectra for symmetrical orthodihalobenzenes including long-range CH couplings

Analysis of high resolution ¹³C NMR spectra for symmetrical orthodihalobenzenes have provided all long-range ¹³CH coupling values in orthodichloro-, dibromo-, and diiodobenzene. Furthermore, since the analyses were sensitive to the sign of the coupling constants, the relative signs of these long-range ¹³CH couplings have been determined from unique spectral fits. The substituent effects on the chemical shifts in this series of compounds appear to be additive. The ¹³CH couplings are compared with coupling values in other compounds and are shown to be related to substituent electronegativity. The absolute magnitude of the ¹³CH couplings for these halogen-substituted compounds are larger than those observed in benzene, with but one exception. In all cases, three-bonded ¹³CH couplings are found to be larger than the two-bond values.     

Hyperfine structure of submillimeter EPR spectra of non-Kramers lanthanide ions in crystals

The hyperfine structures of submillimeter EPR spectra of CsCdBr₃:Tm³⁺ and CaF₂:Dy²⁺ single crystals have been resolved and analyzed. The crystal field parameters and the magnetic hyperfine constants are obtained from fitting the envelopes of the simulated spectra to the measured signals. From the specific peculiarities of the hyperfine structure the energy of the interion interaction in the thulium dimers in CsCdBr₃ is determined. The isotopic shift of the crystal field splitting in energy patterns of dysprosium isotopes in CainF₂ is estimated.     

A pulsed EPR study of the catalytic oxidation of CO over Cu/SnO2

The role of the Cu(II) in the catalytic oxidation of CO over Cu/SnO₂ with low Cu(II) content was studied by continuous wave EPR, electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectroscopes. Three methods were employed for introducing the copper: (i) by coprecipitation, (ii) impregnation onto SnO₂ gel and (iii) impregnation onto calcined SnO₂. Two types of Cu(II) species were identified in these calcined Cu/SnO₂ materials. Those belonging to the first type, termed B and C, exhibit highly resolved EPR spectra with well defined EPR parameters and are located within the bulk of the oxide. The other group comprises a distribution of surface Cu(II) species with unresolved EPR features and are referred to as S. While the latter were readily reduced by CO the former required long exposures at high temperatures (> 673 K). The specific interactions of the different Cu(II) species with CO were investigated through the determination of the¹³C hyperfine coupling of enriched¹³CO. The ESEEM spectra of calcined samples, generated either by coprecipitation or impregnation, show after the adsorption of CO signals at the Larmor frequencies of^{117, 119}Sn and¹³C and at twice these Larmor frequencies. Although these signals indicate that^{117, 119}Sn and¹³C are in the close vicinity of Cu(II), they cannot provide the hyperfine couplings of these nuclei. This problem was overcome by the application of the HYSCORE experiment. The 2D HYSCORE spectra show well resolved cross peaks which provide the hyperfine interaction of these nuclei. Simulations of the HYSCORE spectra yield for^{117, 119}Sn an isotropic hyperfine constant,a _iso, of ±4.0 MHz and an anisotropic component,T _?, of ±2.0 MHz. Pulsed ENDOR spectra also showed^{117, 119}Sn signals which agree with the above values. The¹³C cross peaks yielda _iso=±1.0 MHz andT _?=±2.0 MHz. Similar C cross peaks were observed in spectra of calcined Cu/SnO₂ after the adsorption of CO₂. Based on the same hyperfine couplings in the samples exposed to¹³CO and¹³CO₂ the signals were assigned to surface carbonate species generated by part of the Cu(II) S type species rather then by species B and the role of the Cu(II) in the oxidation process is discussed.     

Mixed valence of iron in natural vonsenite

The exchange of electrons between adjacent ions in different oxidation states in vonsenite was observed using Mössbauer spectroscopy. The Mössbauer spectra of a series of naturally occurring vonsenite were recorded over a temperature range of 120–773 K. Four quadrupole doublets were resolved by computer fitting and assigned to Fe²⁺(Fel), Fe²⁺(Fe3), Fe³⁺(Fe2, Fe4) and Fe²⁺-Fe³⁺(Fe2–Fe4). The percentage of iron sites participating in an electron exchange process increases from 17% between 120 and 298 K to 27% between 573 and 773 K.     

EPR of Marine Diesel

Marine diesel was studied by electron paramagnetic resonance (EPR) spectroscopy at X-(9 GHz) and W-bands (94 GHz). The experiments were performed at room temperature (about 300 K). X-band spectra exhibited isotropy, resolved lines and negligible noise, whereas the W-band spectra exhibited a poorer signal-to-noise ratio and anisotropy in g and in hyperfine interactions. Viscosity at room temperature (2.5 · 10⁻³ kg/m · s) and the tumbling correlation time for free radicals (about 10⁻⁷ s) justified the high mobility of free radicals in marine diesel and consequently, the septet-quartet EPR spectrum of organic radicals with parameters g = 2.0028 ± 0.0005, proton hyperfine couplings A = 6.31 ± 0.01 G (septet) and A′ = 1.80 ± 0.01 G (quartet) at X-band. The perinaphthenyl radicals are probably responsible for the septet-quartet EPR spectrum of this oil by-product. Authors' address: Eduardo Di Mauro, Laboratório de Fluorescência e Ressonancia Paramagnética Eletr?nica, Centro de Ciências Exatas, Universidade Estadual de Londrina, C.P. 6014, CEP 86051-970 Londrina, Paraná, Brasil     

Hyperfine Interaction Tensors of 13C Nuclei for Ring Carbons of Ubisemiquinone-10 Hydrogen Bonded in Alcohol Solvents

The anion radicals of ubiquinones-10 ¹³C chemically labeled at the C₅ or C₆ ring positions in alcohol have been studied by 1D and 2D ESEEM to define the hyperfine interaction tensors with the ¹³C nuclei. Analysis of the cross-peak line shapes and simulations of the spectra allowed us to conclude that the hyperfine tensors are characterized by an anisotropic component T ~6 MHz and an isotropic coupling a ~?3 MHz with support from DFT calculations. However, these values were found to be inconsistent with the shift of the sum combination harmonic in the four-pulse ESEEM spectra. Simulations resolve this apparent discrepancy by showing that the shift of the sum combination to lower frequency and its broadening can be accounted for by a distribution of the hyperfine couplings. A spread of the methoxy group conformations, as supported by previous experimental observations, is suggested as the mechanism influencing the distribution of the hyperfine couplings for the ring carbons.     

Doppler-limited rotational spectrum of the NH radical in the 2 THz region

The Doppler-limited rotational spectrum of the NH radical in its electronic (X) and vibrational ground state has been measured using the frequency stabilized Cologne side-band spectrometer in the frequency region near 2 THz. The nitrogen ¹⁴N nuclear hyperfine patterns have been observed accompanying the resolved fine (J^′←J″) structure of the N=2←1 rotational transition. The observed peak frequencies were analyzed in detail together with the previously measured hyperfine frequencies of the N=1←0 rotational transition and with combination differences obtained from the high-resolution electronic spectra to derive precise rotational, centrifugal distortion, fine, and hyperfine parameters. In the numerical analysis the essential attention has been paid to partly resolved and unresolved hyperfine structures. The peak positions of the partly or fully overlapped lines were analyzed with the help of a profile simulation with estimated half-widths and calculated relative intensities and in this manner the least square fit of the unresolved and partly resolved lines was significantly improved. The NH radical is an extremely important species in nitrogen chemical reaction networks in the interstellar medium and atmospheric chemistry.     

Hyperfine interactions in amorphous and nanocrystalline Fe80Ti7Cu1B12 alloy

⁵⁷Fe Mössbauer spectroscopy is used to elucidate the nature of the hyperfine interactions present in amorphous and nanocrystalline forms of Fe₈₀Ti₇Cu₁B₁₂ alloy. Two mutually independent distributions of hyperfine fields and one sextet of Lorentzian lines are employed to reproduce the broad (atoms in amorphous rest and interface zone) and narrow (ordered) parts of the spectra, respectively. The presented conclusions are derived from three-dimensional mapping of the hyperfine field distributions corresponding to both amorphous and interfacial spectral components. The individual distributions are decomposed into Gaussian components which characterize different types of hyperfine interactions.     

Hyperfine fields and chemical order in Fe-Ge

Films of Fe_0.79Ge_0.21 were synthesized by ion beam sputtering, and were annealed at temperatures from 150 to 500 °C. The as-prepared materials comprised chemically disordered bcc crystallites, but short-range and long-range D0₃ chemical order developed upon annealing. The⁵⁷Fe hyperfine magnetic field distribution can be understood approximately with a model of magnetic response, so the hyperfine magnetic field distribution can be used to follow the changes in chemical short-range ordering. Large local isomer shifts were observed at⁵⁷Fe atoms near Ge atoms.     

Influence of 50 MeV Lithium Ion Irradiation on Hyperfine Interactions of Cr0.5 Li0.5 Fe2O4

Spinel oxide Cr_0.5 Li_0.5 Fe₂O₄ has been irradiated at Nuclear Science Centre, New Delhi, by 50 MeV lithium ions of fluence 5*10¹³ ions/cm² and irradiation effect on hyperfine interactions has been investigated by Mossbauer spectroscopy. The Mossbauer spectrum of irradiated sample shows no paramagnetic doublet contribution and the hyperfine fields corresponding to the Fe³⁺ in the octahedral (B) and the tetrahedral (A) sites are very well separated. That is the observed superimposed A and B sites in unirradiated sample are split into separate lines after Li irradiation. Further an increase of the intensity of the lines (2)–(5) with respect to (1)–(6) signals an orientation of the hyperfine magnetic field towards a direction perpendicular to the ion path due to the irradiation induced strain by the latent tracks. The computer simulation of Mossbauer spectra indicated that the irradiated Fe³⁺-site occupancy of the A-site hyperfine field increased from 43% to 55% whereas the B-site hyperfine field decreased from 57% to 45% compared to unirradiated sample.     

High-frequency EPR of Tb<Superscript>3+</Superscript>-doped KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystal

High-frequency electron paramagnetic resonance (EPR) spectra of the KPb₂Cl₅:Tb³⁺ crystal have been investigated. Three types of spectra were observed in the frequency range of 74–200 GHz. The most intensive spectrum with the resolved hyperfine structure corresponded to transitions between sublevels of the¹⁵⁹Tb³⁺ ground quasi-doublet with the zero-field splitting (ZFS) close to 48 GHz. Experimental results were analyzed by the exchange charge model of the crystal field affecting terbium ions in low-symmetry Pb²⁺ positions with the chlorine sevenfold coordination and the charge compensating vacancy in the nearest potassium site. The calculated values ofg-factors and ZFS were in agreement with the experimental data. The nature of a broad EPR line with ZFS of about 180 GHz and of additional weak EPR lines observed as satellites of the main Tb³⁺ lines was discussed.     

Site-selective electron nuclear double resonance in the exchange-narrowed regime of the ESR in conducting solids

Electron nuclear magnetic double resonance on conduction electrons reveals the hyperfine interaction hidden by the fast electron spin exchange. We used the Overhauser shift technique to investigate the electron spin density of the conduction band of gallium oxide, beta-Ga(2)O(3). Due to the monoclinic structure, the conduction band of beta-Ga(2)O(3) is anisotropic and it is dominated by contributions from the two nonequivalent Ga sites. The large quadrupole couplings of the two gallium isotopes (69)Ga and (71)Ga (both with I = 3/2) are completely resolved in our double-resonance experiments. This resolved quadrupole interaction allows the determination of the electric field gradients at both gallium sites with high precision and high sensitivity. The resolved quadrupole splitting is the key to the site-selected determination of the hyperfine interaction. The concepts behind these double-resonance techniques are rather general and should be applicable in similar semiconductor systems.     

Relaxation effects in the Mössbauer hyperfine structure of amorphous Fe70Co10B20 at 125°C

A new approach was attempted in following the irreversible relaxation effects in the hyperfine structure of amorphous Fe₇₀Co₁₀B₂₀. Room temperature transmission⁵⁷Fe Mössbauer spectra were measured in the course of interrupted isothermal annealing. For the data fitting, a model of pseudo-three-dimensional distribution of correlated hyperfine parameters was adopted and the corresponding spectrum modelled by a FFT-based procedure. In addition to commonly used hyperfine parameters, the second order quadrupole splitting was also considered. The time dependences of the average magnetic and the second order quadrupole splittings show two relaxation stages interpreted as the relief of quenched-in stresses and the free volume shrinking.     

Development of a new method of the analysis mossbauer spectra of systems with nuclear heterogeneity

At present there are two main rival fitting approaches to mossbauer spectra: restoration of hyperfine parameter distribution and discrete deconvolution one. Use of the parallel circuit of processing in which computing procedure the exchange of the calculated values between continuous and discrete algorithms is used for the first time is offered.     

EPR spectra of γ-irradiated hydrated barium dithionate single crystals

EPR spectra of barium dithionate hydrate single crystals γ-irradiated at low (80 Gy) and high (10 kGy) doses are studied. Four lines, the strongest of which is due to the SO₃⁻ radical, are observed in the EPR spectrum of the low-irradiated samples. Another line seems to belong to SO₂⁻. The strong line and weak lines with hyperfine structure and lines for pairs of closely spaced SO₃⁻ centers with a strong angular dependence are observed at high irradiation doses. The main values of the SO₃⁻ hyperfine coupling tensor and the dipole-dipole coupling constants of the SO₃⁻ pairs are determined. A quantum-chemical calculation of the electronic structure of isolated SO₃⁻ and SO₂⁻ radicals is performed. Values of the g tensors and hyperfine couplings are calculated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 18–22, January–February, 2008.