Spin mediator

Coupling constant (J in Hz) Interaction between nuclear spins mediated through chemical bonds giving rise to mutual splitting of resonance lines. 

It is of interest to describe spin systems that are completely different from nitrox-ide-labeled dendrimers, but that also bear in their organic structure a high-spin multiplicity (with S > V) High-spin polycarbenes with ji-conjugation, which are the first and second generations of the spin-mediated dendrimers based on pheny-lacetylenes, were studied by a two-dimensional electron-spin transient nutation (2D-ESTN) method based on pulsed-ESR to determine the spin mulliphcity. The contour plots of the 2D-ESTN spectra of the dendrimer at 3.5 K allowed to identify the nutation frequencies, which were attributed to 4, 4> 4, 3>, 4, 3> <-> 4, 2>, 4, 2> 4, 1>, and 4, 1> 4, 0>. The ESR allowed the detec-... 

Indirect spin u / 1-1Q3 Spin-spin interaction mediated via the bonding electrons through the contact interaction... 

The relationship between mean squared phase shift and mean squared displacement can be modelled in a simple way as follows This motion is mediated by small, random jumps in position occurring with a mean interval ij. If the jump size in the gradient direction is e, then after n jumps at time the displacement of a spin is... 

An intriguing possibility thus presents itself. If some kind of a primordial information, and not higher-level constructs such as mass, energy, spin, and so forth, is indeed the real substance out of which all stuff is made - leaving aside for the moment, the question of form of that information - is it not natural to suppose that a discrete space-time structure, our heretofore pre-defined and static dynamical mediator, is itself built out of the same substance i.e. to suppose that space-time is not just a backdrop for information processing, there only to define what is local and what is not and where to and where from information is allowed to flow, but is itself a construct of primordial information This supposition is not entirely without precedent. 

The process of spin-lattice relaxation involves the transfer of magnetization between the magnetic nuclei (spins) and their environment (the lattice). The rate at which this transfer of energy occurs is the spin-lattice relaxation-rate (/ , in s ). The inverse of this quantity is the spin-lattice relaxation-time (Ti, in s), which is the experimentally determinable parameter. In principle, this energy interchange can be mediated by several different mechanisms, including dipole-dipole interactions, chemical-shift anisotropy, and spin-rotation interactions. For protons, as will be seen later, the dominant relaxation-mechanism for energy transfer is usually the intramolecular dipole-dipole interaction. 

Consider a threaded rod, representing a molecular enantiomer, that lies away from an observer. If the observer reaches out and spins a nut on the rod clockwise with his right hand, the nut will travel forward, away from the observer, and will shortly fly off the rod. Here, the angular momentum imparted to the nut (electron) by the observer s hand (photon) causes it to be ejected in a specific direction from the rod (molecular enantiomer) in the observer s reference frame. This is mediated by the interaction between the chiral thread of the rod and nut (the chiral molecular potential). If the rod is turned through 180° and the action repeated, the nut (electron) still departs in the same direction, away from the observer. Hence, the orientation of the rod (molecule) in the observer s frame does not alter the direction in which the nut (electron) is ejected. 

Now, consider repeating these operations, but with the use of the observer s left hand to spin the nut in an anticlockwise direction as seen by the observer. It should be apparent that, in either orientation of the rod, the nut will now travel backward (toward the observer). This must suggest that an electron would be ejected in a reversed direction following excitation by a photon of opposite helicity, again mediated through the chiral interaction of the electron with the enantiomer s potential field. 

In NiFe204, an inverse spinel Fe +[Ni2+Fe3+]004, the spins of the octahedral sites are parallel with one another the same applies to the tetrahedral sites (Fig. 19.8). The interaction between the two kinds of sites is mediated by superexchange via the oxygen atoms. High-spin states being involved, Fe3+ (d5) has five unpaired electrons, and Ni2+ (ds) has two unpaired electrons. The coupled parallel spins at the octahedral sites add up to a spin of S = + =. It is opposed to the spin of S = of the Fe3+ particles at the tetrahedral sites. A total spin of S = 1 remains which is equivalent to two unpaired electrons per formula unit. 

Bermudez, A., Jelezko, F., Plenio, M.B. and Retzker, A. (2011) Electron-mediated nuclear-spin interactions between distant nitrogen-vacancy centers. Phys. Rev. Lett., 107, 150503. 

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