Magnetic susceptibility corrections

It might appear that a magnetic susceptibility correction would be needed if the susceptibilities of sample and reference differ, but this is not the case. With the field/frequency lock established via the deuterated solvent, the applied magnetic field (H0) simply shifts slightly to maintain the magnetic induction (B0) inside the sample tube constant so as to keep the 2H on resonance. If different deuterated solvents are used for sample and reference, a simple correction must be made for the difference in their 2H chemical shifts. 

There came back an enthusiastic report of a substantial chemical shift difference between the adsorbate and the material in the liquid phase, to be followed shortly by another communication which stated that the difference disappeared when a magnetic susceptibility correction was applied to the results. This illustrates a problem which arises whenever one attempts to measure a chemical shift value in a heterogeneous system, the problem of a suitable reference and of eliminating magnetic susceptibility effects which are particularly troublesome in such systems of dubious geometry. Differences between chemical shifts in the same molecule, if they can be resolved, are... 

The differences (d) of chemical shifts of PEO with and without the potassium iodide are plotted as a function of the chain length (n) in Figure 2. The concentration of PEO and potassium iodide were kept constant for all measurements, and the bulk magnetic susceptibility correction (see later) was also applied. Again, a sharp change is observed atn = 7. 

Fig. 2. Plots of the difference of chemical shifts (with bulk magnetic susceptibility correction) of PEO (1 %) in methanol with and without the potassium iodide (0.05 M) as a function of the chain...

Plots of A values (after the bulk magnetic susceptibility corrections) of 1% PEO-6000 and its monomeric analog, dimethoxyethane, as a function of potassium iodide in methanol are shown in Figure 3. It is obvious that the polymer and its monomeric analog interact differently with the potassium ion when the salt concentration is low further associations of potassium ion with the polymer are reduced by the existing bound ion at higher salt concentrations. In other words, the apparent association... 

The A values of PEO-6000 were also measured in aqueous solutions. They are all zero after the bulk magnetic susceptibility corrections using cyclohexane as standard. 

The gas to be tested may be drawn or forced at the rate of a few cubic centimeters per minute through the test chamber, which in present models has a volume of about 4 ml., or it may be introduced after evacuating the test chamber. The instrument indicates correctly the magnetic susceptibility of the gas in the test chamber within a few seconds the main delay in reading the instrument is caused by the time required to introduce the gas. 

In summary, it is non-trivial to implement magnetic resonance pulse sequences which allow us to monitor unambiguously the decrease in absolute concentration of reactant species and associated increase in product species, but measures of relative concentrations from which conversion and selectivity are calculated are much easier to obtain. However, if such measurements are to be deemed quantitative the spectra must be free of (or at least corrected for) relaxation time and magnetic susceptibility effects. 

Magnetic thermometry 1. Electron paramagnetism 0 001-35 Magnetic susceptibility Curie s law plus corrections l/k T plus corrections ... 

If the electron-cloud radius yrms were exactly equal to the structural radius r, Wasastjerna s criterion would be obviously true. But in fact, for ions r ce. 2 yrms (Table 3). Hence the criterion needs justification. It is obviously most probable for isoelectronic ions (cp. Eauling (/)), but the electron-cloud radii should refer to the ions in the crystals, not to the free ions. For, with a gross difference between crystal and free-ion electron-cloud radii for the hydride ion, there may be significant differences for others 40). For the crystals the electron-cloud radii could be obtained either from polarizeability or from magnetic susceptibility. The theory of polarizeability is less certain and there is a considerable correction to infinite wavelength. We therefore adopt the magnetic evidence. But this must be corrected for the inner shell contribution (Table 3). 

Magnetic Susceptibility Measurements. Magnetic susceptibilities were measured by the Faraday method and were accurate to 2%. Samples, usually as powders, were placed in a cylindrical Teflon boat having an internal volume of 0.30 cc. Measurements were made at 2963, 4357, 5724, 7077, and 8243 G, and at temperatures 77°-295°K. It was possible to correct for ferromagnetic impurities from any field dependent effects. 

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