Electronic magnetic moments, chemically induced

In addition, the external magnetic field induces magnetic moments due to electron circulation in connection with chemical bonds. The observed chemical shift for a given nucleus depends on the orientation of the molecule and of the chemical bond containing the nucleus relative to the magnetic field Bq. In a microcrystalline powder, this chemical bond will have a distribution of orientations relative to the external magnetic field, which leads to... 

A different class of phenomena can be related to the interaction of the electronic polarization density and induced current with the nuclei. Thus the chemical shifts in nuclear magnetic resonance (NMR) spectroscopy are interpreted in terms of magnetic shielding of the electrons, perturbed by a static magnetic field, at those nuclei possessing an intrinsic magnetic moment [7]. 

The most common interactions are dipolar coupling between two spins, chemical shielding and quadrupolar interaction for spins I> 1. The chemical-shielding interaction arises from the motion of electrons around a nucleus induced by the external applied static magnetic field. This motion generates local magnetic fields that modify the total field experienced by the nucleus, and are characteristic of the local chemical environment of the nuclei. All nuclei with a spin /> 1 possess a quadrupolar moment Q that interacts with the EFG Vrs — d2 V/dXfdx at the nuclear site. The EFG tensor Vrs is a symmetric tensor with zero trace Tr( E) = A E = 0 (from Laplace equation). 

Importantly, physical and chemical properties of nanoparticulate films are markedly different from those of the bulk materials. For example, magnetic nanoparticles can be prepared where only one magnetic domain is present, so that the rotation or alignment of the whole particle implies the rotation or alignment of the magnetic moment [53]. Semiconductor nanoparticles possess strong nonlinear optical properties due to increased oscillator strength within excitonic transitions [54-56]. Electrooptical shifts can be induced in metal particles because the surface plasmon band position depends on the free electron concentration electron injection can be used to modulate the peak position [57]. 

There are many experimental techniques for the determination of the Spin-Hamiltonian parameters g, Ux, J. D, E. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detections of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (/iSR). The extraction of data from the spectra varies with the methods, the system studied and the physical state of the sample (gas, liquid, unordered or ordered solid). For these procedures the reader is referred to the monographs (D). Further, effective magnetic moments of free radicals are often obtained from static... 

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