Magnetic Field Spectrum Research Articles

NH-tautomerism effects and isocyclic substitution in alkylporphyrins and their chemical dimers

A study has been made of the absorption spectra, circular dichroism in a magnetic field (MCD), and polarized fluorescence of individual NH-tautomers of free-base porphyrins with asymmetric substitution. The four-orbital model of Gouterman and the perimeter model of Michl have been used in demonstrating that, in spite of the basic differences in type of electronic spectra of the two NH-tautomers of each compound, their absorption spectra in the visible region are described by a system of two linear oscillators X and Y. The fluorescence polarization spectra of the tautomers in the region of band III are extremely sensitive to changes in the side substituents in the isocycle. From an analysis of the sign sequence of electronic bands in the MCD spectra, it has been established that these compounds may be classed as “hard” chromophores with identical type of orbital splitting for the HOMO (b1 and b2) and LUMO (c2 and c2) in the two tautomers of one and the same compound. A specific role has been found for the keto group in the isocycle, as manifested in inversion of the sign sequence of electronic bands in the MCD spectra of NH-tautomers with a cyclopentanone ring.

Large‐scale fluctuations in the solar wind at 1 AU: 1978‐1982

Large‐scale fluctuations (with spacecraft frame periods between several hours and the solar rotation period) in the magnetic field strength B(t) and bulk speed V(t) observed at 1 AU were analyzed using data from IMP 8 and ISEE 3. Most of the power is in the low‐frequency range (3 × 10−7 to 3 × 10−6 Hz). In the intermediate frequency range (3 × 10−6 to ∼3 × 10−5 Hz), the spectra of V(t) and B(t) computed for successive ∼6‐month intervals from 1978 to 1982 had the form f−b, where 〈bB〉 = 1.92 ± 0.06 for the magnetic field spectra and 〈bυ〉 = 1.92 ± 0.10 for the bulk speed spectra. There was no systematic variation of the spectral exponent with time during this interval. A detailed analysis of the bulk speed and magnetic field strength signals was carried out for the data from day 226 to day 365, 1978, which is representative of other such intervals. The spectra of the low‐frequency fluctuations during this interval are essentially the same as those computed from piecewise linear (jump‐ramp) approximations to the speed and magnetic field profiles. The spectra of the intermediate frequency fluctuations during that interval are the result of a superposition of two components: a component due to the jump‐ramp series, which falls off faster than f−2, and a component which falls off slower than f−2. The average width of the jumps in B is 2.2 hours. Twenty‐two percent of the jumps in B have the signature of a forward or reverse shock. The jumps in V are not all simultaneous with the jumps in B. The average width of the jumps in V is 2.1 hours. Thirteen percent of the speed jumps have the signature of a forward or reverse shock.

Quantum oscillations of photothermomagnetic power in two dimensional electron gas at block boundaries in Hg 1−xCd xTe

The photothermomagnetic effect (PTME) in two-dimensional (2D) electron gas at block boundaries in n-Hg 1−xCd xTe single crystals has been investigated. Photothermomagnetic power (V PTM) oscillations caused by quantization of the 2D electron spectrum in magnetic field have been found. It is shown that oscillations of V PTMare determined by oscillations of the derivative of the electron gas density of states in a magnetic field, ∂δ ∂ε F (ε F is the Fermi energy of the 2D gas).

Photoluminescence and magneto-transport of wide InGaAsInP modulation doped quantum wells

A photoluminescence (PL) study of 700Å wide modulation doped InGaAsInP quantum wells in magnetic fields up to 10 Tesla, is reported. PL from the lowest electron sub-bands, localised in the space charge potentials at the two sides of the QW, and from higher delocalised sub-bands extending across the whole width of the QW, is observed. The performance of simultaneous Quantum Hall Effect (QHE), Shubnikov-de-Haas and PL measurements is found to be crucial to obtain a reliable understanding of the behaviour of the PL spectra in magnetic field. In particular the QHE provides direct information on the number of filled sub-bands and Landau levels in a complicated system of total carrier density ∼10 12 cm −2, containing several populated electronic sub-bands.

Three-photon spectroscopy of excitons and polaritons in alkali halides.

Three-photon spectra of nine alkali halides are presented. The nonlinear-optical method of three-photon spectroscopy allows one to measure resonances on the upper polariton branch and the longitudinal exciton at different values of the total k vector. The analysis of the polariton dispersion yields reliable values of the longitudinal-transverse splitting. In Cs halides new exciton lines of ${\ensuremath{\Gamma}}_{5}^{\mathrm{\ensuremath{-}}}$ symmetry are resolved which are forbidden for one-photon optical transitions. In high magnetic fields transitions to paraexcitons of ${\ensuremath{\Gamma}}_{5}^{\mathrm{\ensuremath{-}}}$ and ${\ensuremath{\Gamma}}_{3}^{\mathrm{\ensuremath{-}}}$ symmetry are allowed. The g values for the uppermost valence band and the lowest conduction band are derived from the Zeeman splitting of the paraexcitons and the transverse polariton. In addition, the exchange energy for KI and RbI is gained from the three-photon spectra in high magnetic fields.

Wave normal direction and spectral properties of whistler mode hiss observed on the DE 1 satellite

A new study of magnetospheric hiss as a spatially and temporally enduring phenomenon is undertaken using a recently developed formalism that allows the representation of hiss by a field distribution function (FDF). This formalism explicitly takes into account the whistler mode relationships and the linear and spin motion of the satellite, so that on a spin‐stabilized satellite, it becomes possible to measure the wave propagation direction(s) from the observed fading patterns in the received electromagnetic field data. We have analyzed hiss signals received by electric and magnetic field antennae aboard the DE 1 satellite during a ∼3‐hour period on September 23, 1983. A band of hiss at frequencies <2 kHz was observed continuously from 0236 UT to 0539 UT over a range of geomagnetic latitudes from λm = 45°N to λm = 20°S and L shells of L = 4.3 to L = 5.3. Electron density deduced from in situ and remote measurements indicates that during this time the DE 1 satellite was near the boundary of the plasmasphere. Observations can be summarized as follows: (1) The general character of the electric and magnetic field spectrum remained the same throughout the 3‐hour‐long period, exhibiting an intensity peak at 1550 Hz. (2) The intensities of both the electric and the magnetic field decreased during this interval by ∼30 dB. (3) Well‐defined fading patterns at half the spin period (3.04 s) were observed throughout this period. These patterns were stable over a time scale of ∼1 min. (4) In addition, a slow fading pattern with a time scale of 30 s was observed approximately 30% of the time. (5) The hiss intensity also showed fading over a time scale of ∼10‐15 min. The spin fading patterns led to the measurement of wave propagation direction(s). The results of our analysis can be summarized as follows: (1) Near the geomagnetic equator (within ∼ ±3° latitude) we observe a wave normal angle of 60° ± 5° with respect to the local geomagnetic field. (2) Away from the equator, wave normal directions range from 30° to 80° with respect to the local geomagnetic field. (3) All wave normal directions observed over the 3‐hour‐long period were within ∼ ±45° of the plane normal to the local magnetic meridional plane. Results indicate that the hiss source radiates with initial wave normal angles in the range 30° < θ0 < θg (Gendrin angle) and 90° < ϕ0 < 270°, contrary to the common assumption that the source emits with wave normal angles closely aligned with the geomagnetic field. The FDF formulation has also permitted elucidation of the statistical nature of hiss. The slow time fading (∼30 s) is interpreted in terms of a coherence bandwidth Δω of about 0.2 rad/s.

Measurement of high-resolution NMR spectra in an inhomogeneous magnetic field

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMeasurement of high-resolution NMR spectra in an inhomogeneous magnetic fieldLaurance D. Hall and Timothy J. NorwoodCite this: J. Am. Chem. Soc. 1987, 109, 24, 7579–7581Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://doi.org/10.1021/ja00258a080RIGHTS & PERMISSIONSArticle Views116Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (393 KB) Get e-Alerts Get e-Alerts

Multiple X line reconnection: 3. A particle simulation of flux transfer events

The multiple X line reconnection process, which was proposed by Lee and Fu to explain the flux transfer events observed at the dayside magnetopause, is studied by computer simulations based on a two‐dimensional magnetostatic particle code. A driven boundary condition is applied at the two sides of the simulation domain with an incoming plasma flow while a free boundary condition is used at the other two sides with an outflow. Repeated formation and convection of magnetic islands are observed in the simulation. Magnetic islands with various sizes are observed. Superthermal ions of energy 5–50 keV, with an energy spectrum f(E)∼E−1.9, are generated during the multiple X line reconnection process. It is found that the power spectrum of the normal magnetic field is given by a power law PB ∼ k−0.6, where k is the wave number. The convection speed of magnetic islands may exceed the Alfvén speed. The recurrence time of magnetic islands is found to be τ ≃ 100/ΩRo, where Ω is the ion gyrofrequency, Ro = V1/VA, V1 is the imposed inflow speed, and VA is the Alfvén speed. Our results are consistent with satellite observations of flux transfer events.

Field-induced exchange effects in (Cd,Mn)Te and (Cd,Mn)Se from photoluminescence measurements.

Photoluminescence measurements are made on the semimagnetic semiconductors ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te and ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se for 0<x\ensuremath{\le}0.15. Large energy shifts (\ensuremath{\sim}50 meV) of the exciton recombination peaks and large optical polarizations (\ensuremath{\sim}100%) are produced by applying a magnetic field. This study examines changes in luminescence using magnetic fields up to B=15 T and at temperatures between T=1.5 and 60 K. When viewed along the direction of the field (Faraday geometry), the luminescence due to both exciton recombination and impurity-related transitions becomes circularly polarized. At T=2 K the polarization shows saturation at only 0.5 T.This low saturation field results from the large internal exchange field which produces large spin Zeeman splitting of the bands. We found that the polarization gives a quantitative measure of the exchange effects even when the luminescence features are broader than the splittings. In the Voigt geometry (luminescence observed perpendicular to the magnetic field), the linear polarization gives information on the orbital part of the wave functions of the recombining carriers. Differences in the polarization of the two exciton-related peaks in the (Cd,Mn)Te spectra indicate that one peak arises from an acceptor-bound exciton complex and the second to a simple electron-hole exciton. The latter is attributed to a trapped exciton. With increasing magnetic field, both the (Cd,Mn)Te and (Cd,Mn)Se spectra show splittings of the bound exciton related peaks.At low fields the low-energy feature dominates while at high fields the higher-energy feature is dominant. This is attributed to a field-induced instability of the binding of the exciton to the impurity, resulting from the exchange interaction and Pauli exclusion. At high magnetic fields and low temperature the energy of the exciton peak shows a step in the field-tuning curve. This step reflects a transition of the antiferromagnetically coupled nearest-neighbor manganese ion pair. A value of J/k=-8.4 K is determined for the exchange constant. Finally, the luminescence spectra indicate that samples grown by liquid-phase epitaxy and the traveling-solvent method have much higher purity than Bridgman-grown materials. The manganese concentrations in (Cd,Mn)Te are determined from the energies of the exciton luminescence peaks.

Measurement of high resolution single-quantum J resolved proton spectra in inhomogeneous magnetic fields via zero-quantum coherences

Magnetic field inhomogeneity continues to be a major problem in NMR, particularly in the context of high magnetic field strengths (in absolute, hertz, rather than relative, ppm, terms) and in the context of NMR imaging where the sample volume is large. The only NMR coherence which is intrinsically independent of magnetic field inhomogeneity is zero-quantum coherence (I, 2). Despite the fact that these coherences result in spectra with intrinsic linewidths solely dependent on their spin-spin relaxation times (3), even in an inhomogeneous magnetic field, the utility of the method is compromised because the zero-quantum spectrum does not display the parameters conventionally used in spectral analysis (4). In this communication we demonstrate a pulse sequence whereby zeroquantum coherences can be made to display singlequantum coherence coupling constants at high resolution; this permits the conventional single-quantum coherence spectrum to be reassembled, even when the original data are acquired in an inhomogeneous magnetic field. It is well known that the resonance frequencies and scalar couplings observed in an NMR spectrum are determined by the order of coherence being observed (5) and that these are two of the most important parameters used in spectral analysis. For the chemical shift, the general expression for the precessional frequency of a P-quantum coherence of spins k is given by

Drift wave type turbulence spectrum in a sheared magnetic field

The authors have developed a theory of broad band turbulent spectra of drift wave type instabilities in a sheared magnetic field. They show that different nonlinear processes are involved in determining the spectrum in different wave number ranges: nonlinear shear damping due to three wave resonant mode coupling, ion scattering of beat waves and Hasegawa-Mima (1977) strong turbulence solution. Consequently, the spectrum consists of several appropriately matched subspectra. The presence of an energy sink due to nonlinear shear damping ensures the existence of steady state turbulent solutions.

Mössbauer and molecular orbital (MO) study of localized and delocalized mixed-valence organo-FeIIFeI bisandwiches

A Mossbauer study of two mixed-valence FeIIFeI compounds C5H5Fe(C5H4)2 FeC6(CH3)6 (1) and ¦C6(CH3)6 Fe(C5H4)2 Fe C6(CH3)6¦+ (2+) was carried out from 4.2K to room temperature. Zero-field spectra show two types of iron atoms for1 and one type for2+. Hence1 is a localized mixed-valence complex and2+ a delocalized mixed-valence complexe. High magnetic field spectra for 2+ give a negative sign for the EFG and show the valence electron is delocalized on the two centers. IEHT-MO calculations confirm the results and allow to explain the temperature independence of the quadrupole splitting (QS) of2+.

Use of zero-quantum coherences to measure high resolution n.m.r. spectra in inhomogeneous magnetic fields

The use of zero-quantum coherences to facilitate the measurements of high resolution n.m.r. spectra in an inhomogeneous B0-field is demonstrated using D2O solutions of amino acids.

Spectra of the above-surface magnetic fields predicted by a canonical model of oceanic internal waves

The various fluctuation spectra associated with the magnetic induction field and its spatial derivatives generated by a canonical model of oceanic internal waves are calculated. The calculations are based upon the well-known canonical distribution from statistical mechanics. While in a general ease it is necessary to consider the details of the strong nonlinear interactions between linear internal waves, it is shown that the spectra of the above-surface magnetic fields are independent of such details. The predictions of the canonical model are compared to those of the Garrett-Munk (GM) model. The two models are found to yield significantly different results. An experiment to test the two models is suggested.

Magnetic field properties of Jupiter's tail at distances from 80 to 7500 Jovian radii

A detailed study of the magnetic field data from both Voyager 1 and 2 has revealed interesting properties of the near and distant Jovian magnetotail. During the first encounter, when Voyager 1 passed between 80 and 140 RJ from Jupiter in the near tail and was almost entirely in the northern lobe magnetic field, the field lines were slightly twisted into a right‐handed helix with pitch angle of about 2°–3°. The frequency spectrum of magnetic fluctuations in this region does not appear to be turbulent. A slight tendency of the magnetic field in the distant magnetotail to twist in a right‐hand sense in the northern lobe and left‐hand in the southern lobe is found as far as 7500 RJ downstream in Voyager 2 data. At nearly 7000 RJ the spacecraft was apparently in the magnetosheath near the tail magnetopause, and a 5.3‐hour periodicity in the magnetic field was seen. The magnetic spectra of the distant tail encounters from 6000 to 7500 RJ have power law indices off−5/3, identical to that of solar wind magnetic field spectra at these distances. It is possible that the distant tail magnetic fields have become turbulent, or that solar wind fields from the magnetosheath have diffused into the tail. During one event an interplanetary sector crossing was observed in Voyager 1 solar wind data, as predicted by Kurth et al. (1982). This supports their conjecture that the tail had disconnected from Jupiter. The distant tail spectra from Voyager 2 are also compared with similar spectra obtained from Voyager 1 when it was in near radial alignment with Voyager 2. Limitations of the use of the spectral analysis algorithm in the very low density regions of the Jovian tail also are discussed.

Magnetooptical study of shallow donors in InSb under high pressures

Optical properties of semiconductor quantum dots in magnetic fields are reviewed. A theory is described based on a multi-band effective-mass approximation with a nonparabolic conduction electron dispersion, the direct Coulomb interaction, and the electron-hole exchange interaction taken into account. The transition from the quantum-confined Zeeman effect for a weak magnetic field to the quantum-confined Paschen-Back effect to a strong magnetic field is discussed in comparison with atomic spectra in magnetic fields. Experimental results of the optical properties of isolated CuCl, CdSSe, and Si quantum dots in magnetic fields are also discussed in conjunction with the theoretical results.

Resonant harmonic Alfvén waves in the magnetosphere: A case study

Strong dayside long‐period electric and magnetic field fluctuations were measured on board the geostationary satellite GEOS 2 on April 11, 1979. The electric and magnetic field spectra obtained throughout this day clearly exhibit discrete frequency bands, lasting simultaneously for about 5 hours. The lower‐frequency pulsation with a typical period of 260 s is only present in the electric field data (with typical amplitudes of 0.3 mV/m), whereas the higher‐frequency oscillation dominates the transverse magnetic field spectra (typical period 95 s, typical amplitude 1 nT). The periods of both pulsations increase toward the dusk sector. The observed periods of the pulsations in conjunction with the measured equatorial electron densities, the ratio of the electric and magnetic field amplitudes for both frequency bands, and the constancy of the period ratio yield strong evidence that the two frequency bands represent fundamental and second harmonic mode eigenoscillations of geomagnetic field lines. The mean ratio between the shorter and longer periods derived from the measurements (about 0.35) is slightly different from theoretically obtained ratios, thus indicating shortcomings of currently available models. The phase relationship between the electric and magnetic field fluctuations of the higher‐frequency pulsation, the direction of the wave Poynting vector, and the occurrence of the event after the spring equinox indicate that the major part of the wave energy is fed into the oscillation in the southern hemisphere and not close to the equatorial plane.

Mössbauer study ofMn1−xFexSiin external magnetic fields

The M\"ossbauer effect and the magnetization of ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Si}$ were measured. With increasing FeSi dopant concentration, the weak itinerant-electron ferromagnetism of MnSi disappears around $x=0.15$. M\"ossbauer spectra in magnetic fields were analyzed by taking into account the effect of a ferromagnetic or induced magnetic moment. The external magnetic field induces a hyperfine magnetic field at $^{57}\mathrm{Fe}$ in the nearly ferromagnetic samples ($x\ensuremath{\gtrsim}0.15$).

Hydrogen molecular ion in the magnetic field of a neutron star

A two-dimensional potential energy surface of an H 2 + molecular ion is calculated for the case of the strong magnetic field of the neutron starB=1011–1013 G. It is shown that the dependence of the potential energy from the angle between the magnetic field direction and the internuclear axis becomes very sharp as the magnetic field increases. The obtained potential energy surfaces can be used for studying the vibrational-rotational structure of the H 2 + spectrum in a strong magnetic field and the development of the observational methods for the determination of the magnetic field of a neutron star.

Magnetohydrodynamic Effects of a First-Order Cosmological Phase Transition

The author analyzes the spectrum, amplitude, and evolution of a tangled primeval magnetic field generated by macroscopic dynamo activity arising during a first-order phase transition in the early universe. The effects of the field on the matter distribution at late times could be much larger than that of the adiabatic or isothermal density fluctuations generated by the transition. With optimistic assumptions, magnetic fields generated during a transition at $T\ensuremath{\sim}0.2$ GeV could lead to the collapse of gas clouds of $\ensuremath{\simeq}{10}^{1\ensuremath{-}5}{M}_{\ensuremath{\bigodot}}$ after recombination, and to the formation of pregalactic stars or quasars.