Resonance method

At high frequencies, bridges can still be used, provided that special precautions are taken to eliminate the effects of stray inductances which become very large, but it is usually better to adopt a resonance method above 106Hz. 

At radio frequencies a medium- to low-loss material can be most sensitively examined by making it part of a resonant circuit. The Hartshorn and Ward (1936) method, for which the basic circuit is shown in Fig. 5.11, has been highly developed (Reddish et al., 1971) for very accurate measurements in the 105to 108Hz range. Here a disc specimen is held in a micrometer electrode system (see Fig. 5.6, where the specimen is represented by a capacitance Cx in parallel with a resistance Rx) and connected directly to a coil of fixed 

Circuit analysis shows that the loss tangent of the material is given by 

Measurements may be made at different frequencies by changing the inductance coil. In going to high frequencies the required inductance eventually becomes unpractically small, however, and stray inductances take over. It is then necessary to use a resonant cavity of some kind, and a re-entrant cavity of 

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Measurement of the energy difference is achieved by a resonance method. The population of nuclei in a given state is governed by the Boltzman distribution that leg s to an of nuclei in the state of lowest energy and... 

H. Strehlow, Rapid Reactions in Solution, VCH, Weinheim, Germany, 1992. Recent review of perturbation kinetics and magnetic resonance methods. 

Spectrometric Analysis. Remarkable developments ia mass spectrometry (ms) and nuclear magnetic resonance methods (nmr), eg, secondary ion mass spectrometry (sims), plasma desorption (pd), thermospray (tsp), two or three dimensional nmr, high resolution nmr of soHds, give useful stmcture analysis information (131). Because nmr analysis of or N-labeled amino acids enables determiaation of amino acids without isolation from organic samples, and without destroyiag the sample, amino acid metaboHsm can be dynamically analy2ed (132). Proteia metaboHsm and biosynthesis of many important metaboUtes have been studied by this method. Preparative methods for labeled compounds have been reviewed (133). 

I. I. Rabi (Columbia, New York) resonance method for recording the magnetic properties of atomic nuclei. 

Magnetic resonance methods in the study of the electronic structure of transition metal complexes. 

Magnetic resonance methods include the applications of NMR and EPR spectroscopies. The occurrence of exchange reactions leads to line broadening. The analysis of the line shapes allows the rate constant to be determined. 

Solid state materials have been studied by nuclear magnetic resonance methods over 30 years. In 1953 Wilson and Pake ) carried out a line shape analysis of a partially crystalline polymer. They noted a spectrum consisting of superimposed broad and narrow lines which they ascribed to rigid crystalline and amorphous material respectively. More recently several books and large articles have reviewed the tremendous developments in this field, particularly including those of McBrierty and Douglas 2) and the Faraday Symposium (1978)3) —on which this introduction is largely based. 

From 500° to 760 °K. the impact tube method of Huber and Kan-trowitz (15) used nitrogen containing 0.05% water vapor. Their work on the relaxation of N2 in water yields P(N2 — H20)/P(N2 — N2) = 1100 at 560 °K., and their data are smaller than the calculated values by a factor of 4. The values of Lukasik and Young (17) are obtained from the resonance method between 770° and 1190 °K. using the sample containing <0.005% water. Their values at 1020° and 1186 °K. agree well... 

Porphyrin is a multi-detectable molecule, that is, a number of its properties are detectable by many physical methods. Not only the most popular nuclear magnetic resonance and light absorption and emission spectroscopic methods, but also the electron spin resonance method for paramagnetic metallopor-phyrins and Mossbauer spectroscopy for iron and tin porphyrins are frequently used to estimate the electronic structure of porphyrins. By using these multi-detectable properties of the porphyrins of CPOs, a novel physical phenomenon is expected to be found. In particular, the topology of the cyclic shape is an ideal one-dimensional state of the materials used in quantum physics [ 16]. The concept of aromaticity found in fuUerenes, spherical aromaticity, will be revised using TT-conjugated CPOs [17]. 

This short and far from complete survey shows that the previously obscure field of chemical induction is becoming more and more understood. The accelerating pace of progress has furnished from the forties onwards a great deal of interesting information about the chemistry of unstable intermediates, e.g. chromium(V), chromium(IV), arsenic(IV), tin(III), HO2, OH, SO4 radicals. These results were obtained mostly by conventional methods. Therefore, it may be expected that the more extensive application of methods suitable for detection and estimation of short-living entities (e.g. resonance methods, fast reaction techniques) will enable our somewhat qualitative knowledge (as it is today) to be put onto a quantitative basis. 

P. Blunder, B. Bliimich, R. E. Botto, E. Fuku-shima (eds.) 1998, Spatially Resolved Magnetic Resonance Methods, Materials, Medicine, Biology, Rheology, Geology, Ecology, Hardware, VCH, Weinheim, 774 pp. Collected lectures from an MR imaging conference, various fields, also contains chemical engineering and transport. 

T. Zavada, R. Kimmich 1998, (The anomalous adsorbate dynamics at surfaces in porous media studied by nuclear magnetic resonance methods. The orientational structure and Levy walks), J. Chem. Phys. 109, 6929. 

Nuclear Magnetic Resonance and Electron Spin Resonance Methods X-ray Spectrometry Vol. 2D Coulometric Analysis... 

A major limitation of CW double resonance methods is the sensitivity of the intensities of the transitions to the relative rates of spin relaxation processes. For that reason the peak intensities often convey little quantitative information about the numbers of spins involved and, in extreme cases, may be undetectable. This limitation can be especially severe for liquid samples where several relaxation pathways may have about the same rates. The situation is somewhat better in solids, especially at low temperatures, where some pathways are effectively frozen out. Fortunately, fewer limitations occur when pulsed radio and microwave fields are employed. In that case one can better adapt the excitation and detection timing to the rates of relaxation that are intrinsic to the sample.50 There are now several versions of pulsed ENDOR and other double resonance methods. Some of these methods also make it possible to separate in the time domain overlapping transitions that have different relaxation behavior, thereby improving the resolution of the spectrum. 

The combination of higher fields and pulsed, double resonance methods is now making it possible to use ESR as a tool to determine distances within macromolecules. This is a valuable supplement to the very widespread use of multi-dimensional NMR in structural biology.33... 

From a study of the microwave spectrum of 2-methylselenophene, the second-order Stark effect in the ground state was determined.11 The technique used was double radiofrequency-microwave resonance. For the identification by the double resonance method transitions of chiefly the A-state were chosen. From these observations the components of the dipole moment of 2-methylselenophene and the total dipole moment were determined. 

Numerous new developments and applications of solid state NMR techniques have emerged. Multidimensional NMR methods are able to probe connectivity patterns of zeolite framework structures and solve ambiguities in line assignments [27], high-resolution techniques for quadrupolar nuclei have been developed [31-34], and powerful double-resonance methods permit the study of spatial... 

Additional information can be obtained by employing double resonance methods which probe the dipolar interaction of 29Si and 27A1 within the zeolite framework [93, 94]. The underlying NMR methods will be considered in more detail in Sects. 3 and 4 of this chapter. 

Cf1 - 27A1 or mC H "B triple resonance as well as H 27AI double resonance methods have been employed to measure the local neighborhood between B or A1 nuclei in the zeolite framework and the C (or H) nuclei in the SDA [203]. A set of various boro- or aluminosilicates has been investigated, and Fig. 5 illustrates one of the examples. 

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