Hyperfine Interaction Of Electron Research Articles

Cluster calculation of electronic structure and hyperfine interactions for α-Fe 2O 3

The MSX α cluster technique has been used to study the electronic structure of hematite α-Fe 2O 3, where iron is formally in a 3 d 5 6 S state. The calculated energy levels are compared with X-ray emission and photoelectron spectra. The wave functions have been used to compute the charge distribution, as well as hyperfine parameters such as quadrupole coupling constant, isomer shift and magnetic hyperfine field. The results indicate a considerable influence of chemical bonding on these parameters due to charge transfer and covalency. From the calculated field gradient and the measured quadrupole coupling constant a nuclear quadrupole moment for 57 m Te of about 0.11 b is deduced. This value is smaller than the most recent estimates of 0.15 b based on the ionic model but not as small as the value of 0.082 b obtained from first principles calculations on iron dihalides.

Cluster calculation of electronic structure and hyperfine interactions for garnets

Cluster calculation of electronic structure and hyperfine interactions for garnets

The laboratory millimeter and submillimeter spectrum of HCO

The rotational absorption frequencies of 68 new lines from the HCO radical in its ground electronic state have been measured in the millimeter and submillimeter spectral region. The large zero-field data set acquired has allowed the complex spectrum of this light asymmetric rotor with unpaired electronic spin and magnetic hyperfine interactions to be completely analyzed to within experimental accuracy (<0.1 MHz) for the first time. The wide range of states observed provides a highly accurate map of the rotational frequencies of the formyl radical, which should enable the abundance and excitation of interstellar HCO to be examined in detail.

Electronic structure and hyperfine interaction of muonium in semi-conductors

The Unrestricted Hartree-Fock self-consistent field cluster procedure is being utilized for first-principle investigations of the electronic structures and hyperfine interactions in normal and anomalous muonium states in semi-conductors. Our results for the total energy for the normal muonium state for a twenty-seven atom cluster in diamond, including the muonium and its neighboring atoms, show a minimum at the tetrahedral site and a maximum at the hexagonal site indicating that normal muonium is located in the tetrahedral region and avoids the hexagonal region. Using the calculated spin-density as a function of the position of muonium and carrying out averaging over the vibrational motion of the muon governed by the total energy curve obtained from our work, we have derived a muon hyperfine constant which is about 75% of that in free muonium, in good agreement with experiment. The natures of the total energy and spindensity curves permit us to draw conclusions regarding the origin of the observed trend in the hyperfine constants for normal muonium in diamond, silicon and germanium. The UHF cluster procedure is also applied to study a model of a muon in a positively charged environment for the anomalous muonium center in diamond. This model leads to a hyperfine interaction tensor with the observed feature of strong anisotropy but significantly weaker than experiment. The results obtained for this model indicate the importance for the anomalous muonium state with its relatively weak hyperfine interaction, of exchange polarization effects inherent in the UHF procedure.

Investigation of the electronic structure, hyperfine interactions, and radial densities in the iron tetrahedral sulfides with the use of the multiple-scatteringXαmethod

Spin-polarized multiple-scattering and the Slater $X\ensuremath{\alpha}$ local-exchange calculations have been performed on the tetrahedral Fe${\mathrm{S}}_{4}^{4\ensuremath{-}}$, Fe${\mathrm{S}}_{4}^{5\ensuremath{-}}$, and Fe${\mathrm{S}}_{4}^{6\ensuremath{-}}$ clusters. The calculated charge and spin densities at the Fe nucleus have been used to interpret the M\"ossbauer hyperfine parameters. The calculated energy levels and iron $3d$ and $4s$ population were used to explain the $4s$ contribution, the measured magnetic moment, the observed crystal-field transition, and the large reduction of the free-ion Fermi-contact term.

The millimeter and submillimeter spectrum of HO 2: The effects of unpaired electronic spin in a light asymmetric rotor

An extensive data set for the transient species HO 2 was acquired in the spectral region between 150 and 550 GHz. The complex spectrum of this light asymmetric rotor with unpaired electronic spin and nuclear hyperfine interactions was analyzed and fit to within experimental uncertainty (<0.1 MHz). This work provides, either by direct measurement or well-founded calculation, a map of the rotational transition frequencies of HO 2 over a wide range of states.

Low-energy theorem for electron hyperfine interactions, and the special case of magnetic poles

The $S$-wave scattering length for a Dirac electron passing through a nonsingular magnetic field is shown to be given exactly by lowest-order perturbation theory. (Fermi contact term). In the presence of a pair of Dirac magnetic poles, the result is still correct in the limit of pole separation small compared to the electron Compton wavelength. In the limit of large pole separation, the scattering length takes the form appropriate to the case of a small magnet (whose internal structure is irrelevant) probing the field of the pole pair. In units of the magnetic dipole moment, the effect is half as big and opposite in sign to that in the small-separation limit. The passage from one limit to the other is qualitatively determined, and depends on boundary conditions at the poles. All of these statements depend on the neglect of electric fields, and of higher-order quantum-electrodynamics corrections like the anomalous magnetic moment of the electron.

E.s.r. evidence for chromium (V) porphyrinates

The oxidation of chloro-5, 10, 15, 20-tetraphenyl-porphyrinatochromium(III) with iodosylbenzene proceeds with oxygen transter to chromium and two-electron oxidation of the metal to give a chromium (V) porphyrinate complex; the e.s.r. spectra of this complex, its 17O-derivative, and its t-butylamine adduct show strong electron hyperfine interactions with the metal nucleus and the metal ligands and indicate a metal-centred radical as expected for chromium(V).

Hyperfine-induced singlet-triplet mixing in 3He

We report complete determination of the hyperfine structure of 2 3P and 3 3D states of 3He in which significant singlet- triplet mixing is observed. This mixing arises from the hyperfine interaction of the 1s open shell electron. The interaction is essentially independent of the outer electron; thus unlike the case of one electron-like spectra, the hyperfine interaction is crucial to the electronic structure of highly excited states. Our results allow accurate predictions of the structure of these states.

Electronic structure and hyperfine interactions in tetrahedral alkali-dithioferrates (III) as calculated by the multiple-scattering method

Electronic structure and hyperfine interactions in tetrahedral alkali-dithioferrates (III) as calculated by the multiple-scattering method

Calculation of hyperfine interactions measured by magnetic decoupling in oxygen ions

Magnetic hyperfine interactions in highly stripped oxygen ions recoiling in vacuum have been measured with perturbed angular correlations. The second excited state of16O(I π=3−,E X=6.13 MeV, τ=26.6 psec, |g|=0.55) was produced with the nuclear reactions19F(p,α)16O and16O(α,α′)16O and the angular correlation of the γ-rays observed in coincidence with α particles emitted at 180°. Five recoil velocities between 1.0 and 3.3% c produced average ion charge states from 2.1 to 5.5. The perturbation of the angular correlation and hence the decoupling of the hyperfine interactions was observed as a function of an external axial magnetic field varied between 0 and 33 kG. The perturbation is expected to arise primarily from hyperfine interactions of unpaired 1s electrons with smaller contributions from 2s electrons and other configurations. The maximum external field was strong enough to decouple all hyperfine interactions except that of the 1s electrons. The decoupling curves obtained were successfully fitted by calculations using the hyperfine interactions of the pertinent atomic Hartree-Fock-Slater orbitals.

Classification of the External Magnetic Field Effects on the Photodecomposition Reaction of Dibenzoyl Peroxide

Abstract The external magnetic field effects upon product yields in the singlet sensitized photolysis of dibenzoyl peroxide in toluene were studied. The observed field dependencies were classified into four types, and were interpreted in terms of the electronic Zeeman and hyperfine interactions in the intermediate radical pair. Especially large magnetic field effects were observed for the yields of dimethylbiphenyls, new products in this reaction.

Electronic structure and hyperfine interactions in the FeO42−ion

Self-consistent-field $X\ensuremath{\alpha}$-scattered-wave calculations were performed for the ferrate ion (Fe${\mathrm{O}}_{4}^{2\ensuremath{-}}$) in spin-restricted and spin-unrestricted schemes. Valence ionization energies are obtained and compared to experimental values. The charge and spin densities at the Fe nucleus derived from these calculations are related to M\ossbauer-isomer-shift and hyperfine-field values. Results show that the occupation of the $3d$ orbital is much higher than in the formal $3{d}^{2}$ configuration, but the effective number of unpaired electrons is less than two.

Electronic Structure and Hyperfine Interactions in α‐Fe‐Based Dilute Solid Solutions

Electronic Structure and Hyperfine Interactions in α‐Fe‐Based Dilute Solid Solutions

Study of variation in properties of ferric porphyrins with fifth ligands—magnetic hyperfine interactions

The electronic structures and magnetic hyperfine interactions in a series of related heme compounds have been studied. Four of these are high spin ferric heme compounds with different fifth ligands, namely, fluoride, chloride, bromide, and hydroxide, and the fifith is a low spin cyano–ferric–heme compound. The molecular orbitals needed in the calculation were obtained by the self-consistent charge extended Hückel method. For the four high spin ferric compounds the hyperfine constants of 57Fe and 14N nuclei were found to vary only 4% among themselves. In the chloride derivative, the only one for which 57Fe data are available, excellent agreement was found between our result and the 57Fe hyperfine field in hemin from Mössbauer measurements. For 14N nuclei in the fluoride, chloride, and bromide derivatives the near constancy of the predicted hyperfine constants is borne out experimentally, with the theoretical values being all about 50% of experiment. For the low-spin cyano compound we predict the 57Fe hyperfine field per spin to be 60% larger than the corresponding fields in high spin heme derivatives, while the hyperfine field at 14N per spin is substantially smaller than its counterpart in the high spin compounds. Our results for the hyperfine fields in the series of compounds studied and their agreement with available experimental data demonstrate that there is substantial delocalization of unpaired spin away from iron for these ferric heme compounds, especially the high spin ones. This feature is also supported by a similar calculated decrease in the iron 3s core energy splittings relative to that expected in free Fe+3 ion, which is verified by ESCA measurements in hemin chloride. The need for additional experimental data on the hyperfine fields, particularly for 57Fe and 14N in the cyano compound, is stressed.

Rapid Decay Mechanisms for Bulk Spin-Aligned Atomic Hydrogen atT=0K in Large Magnetic Fields

Solid spin-aligned atomic hydrogen is shown to be unstable against spontaneous magnon creation due to electronic dipole-dipole and hyperfine interactions even at $T=0$ K for magnetic fields less than ${H}_{c}\ensuremath{\approx}\frac{7.3\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{J}}{{\ensuremath{\mu}}_{e}}$, where $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{J}$ is the motionally averaged exchange interaction. For an fcc crystal at 50 ${\mathrm{cm}}^{3}$/mole, ${H}_{c}\ensuremath{\approx}{10}^{6}$ G. Similar considerations apply to the fluid state where the relevant parameter is again $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{J}$ which is proportional to the density in the low-density limit.

Behavior of the13C lines in the ESR spectra of 3,6-di-tert-butyl-2-oxyphenoxyl with intramolecular hydrogen atom migration

1. Study has been made of the effect of unpaired electron hyperfine interaction with the13C nucleus on the ESR spectrum of 3,6-di-tert-butyl-2-oxyphenoxyl. 2. The spin density distribution has been calculated for the radical under both rapid and slow exchange, and13C hfi constants obtained for various positions.

Electronic structure and hyperfine interactions for hydrazyl radicals

Some aspects of electronic structure and hyperfine interactions for α,α-diphenyl-β-picrylhydrazyl and its derivatives have been studied. High resolution EPR spectra have been obtained and analyzed by the least-quares method in Fourier space. The results obtained are confirmed by NMR experiments. Anisotropic EPR spectra of hydrazyl radicals in frozen solutions and glasses have been recorded. Parameters of hyperfine tensors and g-tensor have been determined by the least-squares method. Spin distributions in radical molecules are calculated by the unrestricted Hartree—Fock method and calculations of isotropic and anisotropic hyperfine interactions have been carried out.

Electron paramagnetic studies of nitric oxide haemoglobin derivatives: Isolated subunits and nitric oxide hybrids

The electron paramagnetic resonance spectra of various nitrosyl-haemoproteins have been studied at room temperature and at 77 °K. A detailed investigation of the isolated α NO, β NO> and γ NO chains of human haemoglobins has led to the description of new spectral features. These are tentatively assigned in terms of paramagnetic centre symmetry and of the hyperfine interactions of unpaired electrons with the nitrogen nuclei of the proximal histidine and the liganded nitric oxide. Furthermore, electron paramagnetic resonance spectra are described for various haemoglobin nitric oxide hybrids in which one type of chain is liganded to NO and the partner chain can take a variety of ligation and valency states, namely ferrous (deoxy, oxy and carboxy) or ferric (aquo, fluoride, azide and cyanide). The electron paramagnetic resonance spectra at 20 °C and 77 °K of the α NO β hybrids are found to depend on the spin state of the haem carried by the β chain: for low spin, the spectra are identical to those of the free α NO subunit; for high spin, the spectra are modified. Such modifications are generally assigned to an alteration of the d z2 — σ∗ molecular orbital containing the unpaired electron. By contrast, the electron paramagnetic resonance spectra of the αβ NO hybrids were always identical to those of the isolated β NO subunits, independently of the spin state of the α haem. The results are discussed in the light of the subunit non-equivalence and of the importance of the haem spin state changes in the mechanism of haem-haem interaction.

Studies of OH− and OD− Ions in Magnesium Oxide. II. The Structure of the VOD Center

This paper reports EPR, ENDOR, and infrared absorption measurements on the VOD center in MgO. The magnetic properties are well fitted to a spin Hamiltonian which includes terms due to electronic Zeeman, nuclear Zeeman, and hyperfine and nuclear quadrupole interactions. The magnitude of the unpaired electron spin density at the deuterium nucleus is similar to that for the hydrogen nucleus in the VOH center. Infrared absorption due to the fundamental stretching vibration of the O–D− bond in the VOD center occurs at 2464.5 cm−1. The oscillator strength of this vibrational transition is small, being of order 10−2. The analogous stretching frequency of the OH− bond in the VOH center in CaO is observed at 3447 cm−1.