Nuclear spins resonance

Isotope Nuclear spin Resonance frequency, MH2 Relative sensitivity Magnetic moment, 10 j/t ... 

Still another type of spectroscopy was added to the chemist s bag of tricks in 1946. In principle, it is similar to electron spin resonance, but it, is based on the spins of atomic nuclei, rather than electron spin. Nuclear spin resonance (or, as it is more often called, nuclear magnetic resonance) developed phenomenally in the 1950 s, and today it is a versatile source of structural information. 

A most interesting application of nuclear spin resonance spectroscopy is the study of very fast reactions, particularly the transfer of hydrogen ions from one species to another. In the acid base equilibrium... 

Tiers, G. V. D. Fluorine nuclear spin resonance. Part III. The slow con-... 

ESR occurs at a much higher frequency than the NMR in the same magnetic field, because the magnetic moment of an electron is about 1800 times that of a proton. ESR is observed in the microwave region (9-38 GHz), nuclear spin resonance at radio frequencies (10-950 MHz). 

Crysts of NaNj-3HjO were isolated by Wohlgemuth (Ref 60). Cranston Livingstone (Ref 30) and GUnther Perschke (Ref 46) detd densities, refractive indices and elec conductivity of aq NaNj solns the electrolysis also was studied by Turrentine (Ref 11), Briner Winkler (Ref 24), Schmidt (Ref 140) and by Semenchenko Serpinskii (Ref 58), Audubert et al (Refs 82 87), Verdier (Ref 93)) and Jolibois Clerin (Ref 95) mol refraction by Petrikalns Ogrins (Ref 79), optical props by Angstrom (Ref 13). From his studies of the props of aq NaNj solns, Yui (Ref 88) detd the true dissociation constant of HNj. Nuclear spin resonance of aq NaNj and other Na compds has been reported in Ref 187... 

In spite of the great number of measurements of the properties of this compound, including conductivity, dielectric constant, magnetic susceptibility, electron and nuclear spin resonance, specific heat, thermoelectric power, etc., many over wide temperature and frequency ranges, there is still no consensus as to how all the various pieces of the puzzle fit together. Even such a basic question as to whether most of the high temperature conduction is along the TTF or the TCNQ stacks or in hybridized orbitals of both remains open. 

These two results will be analysed below in terms of the model of motional or exchange narrowing, which was originally developed by Anderson [12] as well as by Kubo and Tomita [13]. This model is the basis of many methods in magnetic resonance, in particular in nuclear-spin resonance. It was treated in detail theoreti-... 

A well-known and important phenomenon in the area of nuclear-spin resonance (NMR) in gases, liquids, or solid samples is dynamic nuclear-spin polarisation (DNP) (see e.g. [M6]). This term refers to deviations of the nuclear magnetisation from its thermal-equilibrium value, thus a deviation from the Boltzmann distribution of the populations of the nuclear Zeeman terms, which is produced by optical pumping (Kastler [31]), by the Overhauser effect [32], or by the effet solide or solid-state effect [33]. In all these cases, the primary effect is a disturbance of the Boltzmann distribution in the electronic-spin system. In the Overhauser effect and the effet solide, this disturbance is caused for example by saturation of an ESR transition. Owing to the hyperfine coupling, a nuclear polarisation then results from coupled nuclear-electronic spin relaxation processes, whereby the polarisation of the electronic spins is transferred to the nuclear spins. 

Azz is the component of the hyperfine tensor in the Bq direction. Avesr is called the Overhauser shift. It is analogous to the Knight shift Avnmr of tho nuclear-spin resonance frequency v mr in the presence of conduction electrons with a polarisation P. ... 

The Overhauser shift is very small the contribution to Avesr/ esr of the protons is of order 10" and that of less abundant nuclear spins, e.g. is of order 10" [34]. Their measurement is accomplished by a double resonance technique. The shift A Bov of the resonance field for ESR is measured at a constant ESR-microwave frequency vesr (e.g. 9.4 GHz), while at the same time a strong radio-frequency field with the variable frequency Vjfis applied. When Vjf= v mr the nuclear-spin resonance, e.g. the nuclear-spin resonance of the protons at Vrf=Vp, will be saturated. This produces equal populations of the two nuclear-spin Zeeman levels, causing the nuclear-spin polarisation P to vanish. This leads according to Eq. (9.27) to a shift of the ESR resonance field by an amount... 

Figure 9.23b shows the experimental result for saturation of the proton-spin resonance in a (Fa)2PF6 crystal the spectrum ABov( rf) is the indirectly measured nuclear-spin resonance line of the protons. From the absolute value of ABqv at the maximum, that is at the proton-spin resonance frequency Vp, applying Eq. (9.29), the average hyperfine coupling Azz of all the protons can be directly determined. Similar experiments were carried out with nuclei [34]. 

Bovey, F. A. Tiers, G V. D. Polymer nuclear spin resonance spectroscopy. 11. The high-resolution spectra of methyl methacrylate polymers prepared with free radical and anionic initiators. J. Polym. Sci. 1960,44,173-182. 

Experimentally, we do not have any data on the diffusion of trapped chains in a network. What is available is the diffusion coefficient of a labeled chain in polyethylene melts, measured by two techniques 1) from nuclear spin resonance data, and 2) using deuterated chains as labels, the local concentrations of deuterated/protonated species being probed by infrared measurements. ... 

Dynamic magnetic susceptibilities as measured by electron-spin resonance, nuclear-spin resonance and inelastic neutron scattering experiments... 

Intense THz magnetic field pulses allowed not only the induction of spin precession but also its extinction on demand. This was achieved by exciting the sample by a pair of THz pump pulses which were delayed with respect to one another the second, delayed pulse induced a precessional motion that was out of phase with the precession due to the first pulse, and thereby stopped the spin precession. This is shown in Figure 6.15(e) for a pump pulse pair delayed by 6.5 precession cycles. Similar sequences of pulses (of much lower frequencies) have been used in nuclear spin resonance to investigate molecular structure. The extension to the THz domain (THz-ESR) would require, however, magnetic field strengths about 100 times stronger than currently available in the Department. 

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