Theoretical study of magnetic properties of ammonia molecule in nonuniform magnetic field

The interaction Hamiltonian within the Bloch gauge for the potentials of the electromagnetic field has been used to define magnetic multipole moment operators and operators for the magnetic field of electrons acting on the nuclei of a molecule in the presence of nonhomogeneous external magnetic field. Perturbation theory has been applied to evaluate the induced electronic moments and magnetic field at the nuclei. Multipole magnetic susceptibility and nuclear magnetic shielding tensors have been introduced to describe the contributions arising in nonuniform fields, and their origin dependence has been analyzed. Extended numerical tests on the ammonia molecule in a static, nonuniform magnetic field have been carried out, using the random-phase approximation within the framework of accurate Hartree-Fock zero-order wavefunctions, and allowing for both angular momentum and torque formalisms in the calculation of paramagnetic contributions.     

强磁场辅助TFA-MOD法制备YBCO厚膜的理论分析

为了实现YBa2Cu3O7-x(YBCO)涂层导体在电力工业中的实际应用，必须有效增加YBCO超导层的厚度。提出一个强磁场辅助TFAMOD法制备YBCO厚膜的新工艺，并从磁热力学和磁性物理出发理论分析其可行性。沿垂直基底平面方向施加强磁场时，磁场将促进c轴取向YBCO晶核的形成，诱导厚膜中非c轴取向晶核转动到c轴平行磁场取向的位置。另外，取向晶粒间磁性相互作用力使晶粒沿磁场方向定向聚合，有利于获得致密的厚膜。因此，强磁场辅助TFA—MOD法有望制备高临界电流密度的YBCO织构厚膜。     

Diatropicity of tetraazanaphthalenes

Tetraazanaphthalenes are diatropic molecules, whose magnetic response to a magnetic field perpendicular to the molecular plane closely resembles that of naphthalene. The out-of-plane component of the magnetic susceptibility tensor and its strong anisotropy can be used as quantifiers of magnetic aromaticity. Maps showing streamlines and modulus of the current density field provide clear evidence for diatropicity of these systems. They also explain the strong anisotropy of carbon and nitrogen magnetic shielding, which is determined by the big out-of-plane component of the nuclear shielding tensor. The electronic ring currents observed in the map deshield the nuclei of ring hydrogens by enforcing the local magnetic field and diminishing the out-of-plane component of proton shielding.     

Theoretical study of the magnetic properties of an SF6 molecule in non-uniform magnetic field

Perturbation theory has been applied to evaluate the induced electronic moments and magnetic field at the nuclei of an SF₆ molecule interacting with an external magnetic field with a spatially uniform gradient. Contributions to magnetic susceptibility and magnetic shielding of the nuclei have been evaluated using the random phase approximation within the framework of accurate Hartree-Fock zero order wavefuctions. The quality of the calculations has been judged by the fulfillment of sum rules for the origin dependence of the response properties.     

Connection between the nuclear electric shielding tensor and the infrared intensity

The integrated IR intensity can be directly related to the electric shielding tensor of the nuclei in a molecule. This allows us to measure, by IR spectroscopy, the effective electric field at the nuclei of a molecule immersed in an external electric field. Relations exist with the dynamic polarizability and the magnetizability, which implies the possibility of a unified treatment of electric and magnetic second-order properties.     

Magnetic properties of a molecule in non-uniform magnetic field

Summary The potentials of the electromagnetic field in the Bloch gauge are used to obtain definitions for the multipole moment operators and for the operators expressing the electric and magnetic field of electrons acting on the nuclei of a molecule. Perturbation theory is employed to determine induced electronic moments and total electromagnetic field at the nuclei. A series of response tensors is defined to describe the contributions arising in non-uniform magnetic field and their origin dependence is studied.This paper is dedicated to Professor Werner Kutzelnigg on the occasion of his 60th birthday     

Solution-state dynamic nuclear polarization at high magnetic field

The goal of dynamic nuclear polarization (DNP) is to enhance NMR signals by transferring electron spin polarization to the nuclei. Although mechanisms such as the solid effect and thermal mixing can be used for DNP in the solid state, currently, the only practical mechanism in solutions is the Overhauser effect (OE), which usually arises due to dipolar relaxation between electrons and the nuclei. At magnetic fields greater than approximately 1 T, dipolar relaxation does not result in a useful enhancement and therefore the conventional wisdom is that DNP should not work in solutions at high magnetic fields. However, scalar relaxation due to time-dependent scalar couplings has a different magnetic field dependence and can lead to substantial OE enhancements. At room temperature and at a magnetic field of 5 T (211 MHz for protons, 140 GHz for electrons), we have observed that scalar relaxation between electrons and nuclei results in NMR signal enhancements of 180, 42, -36, and 8, for 31P, 13C, 15N, and 19F, respectively.     

氢核磁共振谱自旋耦合裂分现象的量子力学解释

Hydrogen nuclear magnetic resonance spectroscopy (¹H-NMR) is an important content in the university course of instrumental analysis and organic structure analysis. The splitting law of spin coupling between hydrogen nuclei is the focus of teaching and learning. Most textbooks explain that the cause of spin coupling splitting is due to the local magnetic field produced by the different spin orientation of other adjacent nuclei (nuclei magnetic dipole-dipole interaction, direct nuclear spin coupling), and a few monograph on Nuclear Magnetic Resonance refers to electron spin polarization mediated nuclear spin coupling (indirect nuclear spin coupling). Here we introduce quantum mechanics for explanation of the splitting law of spin coupling between hydrogen nuclei.     

Vortices and their relation to ring currents and magnetic moments in nanographenes in high magnetic field

Much attention has been paid to the role of vortices in the magnetic response properties of superconductors, but less so for molecular systems. Here we present a theoretical analysis on nanographenes subject to a strong homogeneous magnetic field. The analysis is based on the simple Hückel-London model, for which we derive the topological definition of vorticity. The results are confirmed by a more elaborate model that includes nonnearest neighbor interaction, the explicit presence of nuclei and all terms due to the magnetic field. We find that due to frontier orbital intersections, large changes in magnetic dipole moments occur. Orbital energy minima and maxima can be related to change of vortex patterns with flux.     

DNP sensitivity of 19F‐NMR signals in hexafluorobenzene depending on polarizing agent type

Low field dynamic nuclear polarization or low field magnetic double resonance technique enables enhanced nuclear magnetic resonance signals to be detected without increasing the strength of the polarizing field. The study reports that the dynamic nuclear polarization of ¹⁹F nuclei in hexafluorobenzene solutions doped with nitroxide, BDPA, MC800 asphaltene and MC30 asphaltene free radicals at 15 G. The ¹⁹F nuclei in all solutions gave positive DNP enhancements changing between 3.42 and 189.54, corresponding to predominantly scalar interactions with the unpaired electrons in the radicals. DNP sensitivity of ¹⁹F nuclei in hexafluorobenzene was observed to be changed significantly depending on the radical type. Nitroxide was found to have the best DNP performance among the polarizing agents. Copyright © 2016 John Wiley & Sons, Ltd.     

A stochastic model for transient magnetic fields as observed by perturbed angular distribution of gamma rays

A stochastic model is introduced to study the transient magnetic field (TF) experienced by the nuclei of fast ions traversing a ferromagnetic medium. The field is assumed to arise primarily from the bound electrons of the ion, polarized by the internal magnetic field of the ferromagnetic specimen. Spin-flip scattering is considered to be the dominant mechanism for polarization transfer from the host to the ion. Electron capture and loss mechanisms are also taken into account in a phenomenological manner. An analytical expression is derived for the TF which depends on the electron capture and loss cross-sections. The result for the perturbation factor is shown to be more general than that derived by Abragam and Pound and reduces to their result in the appropriate limit.     

Magnetic field affects enzymatic ATP synthesis

The rate of ATP synthesis by creatine kinase extracted from V. xanthia venom was shown to depend on the magnetic field. The yield of ATP produced by enzymes with 24Mg2+ and 26Mg2+ ions in catalytic sites increases by 7-8% at 55 mT and then decreases at 80 mT. For enzyme with 25Mg2+ ion in a catalytic site, the ATP yield increases by 50% and 70% in the fields 55 and 80 mT, respectively. In the Earth field the rate of ATP synthesis by enzyme, in which Mg2+ ion has magnetic nucleus 25Mg, is 2.5 times higher than that by enzymes, in which Mg2+ ion has nonmagnetic, spinless nuclei 24Mg or 26Mg. Both magnetic field effect and magnetic isotope effect demonstrate that the ATP synthesis is an ion-radical process, affected by Zeeman interaction and hyperfine coupling in the intermediate ion-radical pair.     

List of Subjects

It has been shown that the presence of magnetic nuclei with sufficiently high hfi constants in radicals can affect the CIDNP of the other nuclei so that the spin polarization sign can alter and become opposite to that predicted by the Kaptein rules. This mutual nuclear effect on the CIDNP reduces with increasing external field strength and radical acceptor concentrations.     

Understanding the ring current effects on magnetic shielding of hydrogen and carbon nuclei in naphthalene and anthracene

The local response to an external magnetic field normal to the molecular plane of naphthalene and anthracene was investigated via current density and magnetic shielding density maps. The Biot-Savart law shows that the deshielding caused by pi-ring currents in naphthalene is stronger for alpha- than for beta-protons due to geometrical factors. The shielding tensor of the carbon nuclei in both molecules is strongly anisotropic and its out-of-plane component determines the up-field chemical shift of (13)C in nuclear magnetic resonance spectra. The pi-ring currents flowing beyond the C-skeleton in front of a probe carbon nucleus, and on remote parts of the molecular perimeter, yield positive contributions to the out-of-plane component of carbon shielding as big as approximately 10-15% of the total values. Near Hartree-Fock estimates of magnetizability and magnetic shielding at the nuclei fully consistent with the current model are reported.     

Magnetic field effects on the thermodynamic and kinetic parameters of intercalation of gallium selenide with nickel

The magnetic field effect on the thermodynamic and kinetic parameters of the formation of Ni _x GaSe intercalates became significant at nickel concentrations that provided interaction between the magnetic moments of the guest and the formation of supermagnetic phase nuclei. This interaction in Ni _x GaSe and the Zeeman delocalization of current carriers at room temperature increased the free energy of intercalation in a magnetic field. The highest resistance at the charge transfer stage of intercalation of gallium selenide with nickel was obtained for two-phase states without a magnetic field. The maximum change in the energy relief for charge transfer in Ni _x GaSe intercalates obtained in a magnetic field was recorded for high values of x in onephase regions, in which there were temperature neighborhoods of the inversion of the temperature coefficient of specific resistance, which coincided with a substantial increase in the real part of dielectric permittivity and correlated with the distinct maximum of dielectric permittivity measured at extra low frequencies. Original Russian Text ? N.T. Pokladok, I.I. Grigorchak, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 575–579.     

固态Photo-CIDNP效应

光化学诱导动态核极化(photo-CIDNP)是一种在光照条件下由于产生非玻尔兹曼核自旋极化而使核磁共振(NMR)波谱信号强度发生明显变化的效应。这种效应在液体NMR中已为人所熟知,并通过经典的自由基对机理得到解释。固态photo-CIDNP效应发现的较晚,本文介绍了在光合反应中心及蓝光受体中发现的固态photo-CIDNP效应,详细阐述了固态photo-CIDNP效应产生的自由基对自旋动力学的机理,包括三旋混合(TSM)、衰变差异(DD)和弛豫差异(DR),重点介绍了类球红杆菌光合反应中心固态photo-CIDNP效应的磁场依赖性,这种场依赖性在同一分子中的不同核之间表现出明显的差异。本文综述了固态photo-CIDNP效应的现象、理论及其磁场依赖特性的最新进展。     

Spatial ring current model for the prismane molecule

Spatial models of magnetic-field induced electronic ring currents have been constructed for the prismane molecule via stagnation graphs and current density maps. These tools provide an insight into the complicated phenomenology resulting from competition of diatropic and paratropic regimes that determine the magnitude of various components of magnetic susceptibility and magnetic shielding of hydrogen and carbon nuclei. Shielding density maps show that the differential Biot-Savart law, along with an atlas of the current density field, explains magnetic shielding at hydrogen and carbon nuclei and virtual shielding at ring and cage centers.     

Stark effect on the nuclear quadrupole resonance of n in an asymmetric field gradient: I. Line shape

Nuclear quadrupole resonance line shapes in the presence of the Stark effect were studied in the case of asymmetric field gradients, where the exciting magnetic field forms an arbitrary angle with the electric field. This study was performed in order to interpret ¹⁴N resonance results but it can also be extended to other nuclei.     

Nanosecond time-resolved magnetic field effect on radical recombination in solution

The time dependence of the magnetic field effect on radical recombination in solution has been analyzed experimentally and theoretically. For the geminate recombination of anthracene anions and dimethylaniline cations in a polar solvent, the effect originates from a magnetic field dependent production of triplet states in an initially singlet phased radical pair, induced by hyperfine interaction of the unpaired electrons with the nuclei. The magnetic field dependence of the triplet yield shows a lifetime broadening of the energy levels of the radical pair if a short delay-time between radical production and triplet observation is chosen. The agreement of this delay-time dependent broadening effect with the theoretical results proves directly the coherence of the spin motion in the radical pairs.     

Sensitive through-space dipolar correlations between nuclei of small organic molecules by partial alignment in a deuterated liquid solvent

Through-space residual dipolar correlations in NMR spectra can be measured between nuclei of small organic molecules by partially aligning them with respect to the magnetic field in a pure deuterated liquid solvent, 4-pentyl-4'-cyanobiphenyl. A simple temperature change of this liquid phase enables spectra to be compared between samples under isotropic tumbling conditions and weakly oriented anisotropic states. This should provide access of a number of small nonpolar molecules to more sensitive through-space nuclear correlations than possible through NOE experiments, depending on the net orientation of specific nuclear pairs with respect to the magnetic field and the specific coherence transfers employed.