Gyromagnetic ratio


Sometimes called the gyromagnetic ratio. For a free electron = 2-003.  [c.189]

Electron Spin Resonance. Electron spin resonance (esr) also known as electron paramagnetic resonance (epr) is a second magnetic resonance technique which finds particular appHcations in the study of free radicals, paramagnetic species, and other molecules containing an unpaired electron. The electron has a spin of 1/2 and, because of its low mass, a gyromagnetic ratio of 1760 rad/ (T-s). Eield strengths required for esr are much lower, typically 0.34 T (3.4 kG) and the frequencies higher (9—35 GHz) than for nmr. Data are usually reported in terms of intensity, signal strength, versus energy where the energy for a transition is usually expressed as  [c.400]

Electron Spin Resonance. Instmmentation for esr differs from nmr instmmentation principally as a consequence of the larger gyromagnetic ratio in this experiment. As a result, the external field is typically 0.35 T (3.5 kG). At this field strength the frequency associated with an unpaired electron is about 9.5 GHz (X-band). Systems operating at frequencies up to 34 GHz ( -band) are also available. Fourier transform is becoming commonplace, but CW instmments also are widely used. Microwave radiation at a fixed frequency is produced by a Klystron valve at power levels ranging from less than 0.1 )J.W to several hundred mW and transmitted to the sample via rigid waveguides rather than the coaxial wire. The waveguide terminates in a reflection resonance cavity controlled by a microwave bridge. The function of this cavity is to focus the energy on the sample (see Microwave technology). In comparing systems, reference is made to the Q factor, ie, the ratio of the energy stored in the cavity to the energy lost in a cycle. Q factors of 5000—7000 are common. Esr signals typically become stronger at lower temperatures, and variable temperature systems capable of approaching Hquid helium temperatures are available. Data are plotted in most appHcations as the first derivative spectmm. This presentation is more sensitive to changes in hyperfine stmcture than the absorption mode. Many esr spectrometers are also equipped to connect the electron nuclear double resonance (endor) experiment (9), which requires that the instmments supply rf at both the electron and nuclear frequencies.  [c.402]

The proportionahty constant y is called the gyromagnetic ratio which is a function of the magnitude of the nuclear magnetic moment. Therefore each isotope having a net nuclear spia possesses a unique y. The y of some biologically relevant nuclei can be found ia Table 3.  [c.53]

Proton gyromagnetic ratio vp 26752.2128(81) 104 s-iT- 0.30  [c.1343]

Because the energy differences between adjacent levels are very small in magnetic resonance experiments, the transition probabiUties are also very small in the absence of local field fluctuations. Dipole—dipole interactions are the dominant mechanism for creating local field fluctuations and these decrease in intensity with the sixth power of the intemuclear distance, so that only the closest nuclei have an appreciable effect on the relaxation rate for a given atom. The strength of the interaction also depends on the square of the product of the gyromagnetic ratios of the interacting nuclei. Other mechanisms, such as quadmpolar relaxation, may become important if either of the interacting nuclei is paramagnetic or the quadmpolar moment (see Table 1) is significant.  [c.400]

Figure 8 Effects of spin diffusion. The NOE between two protons (indicated by the solid line) may be altered by the presence of alternative pathways for the magnetization (dashed lines). The size of the NOE can be calculated for a structure from the experimental mixing time, and the complete relaxation matrix, (Ry), which is a function of all mterproton distances d j and functions describing the motion of the protons, y is the gyromagnetic ratio of the proton, ti is the Planck constant, t is the rotational correlation time, and O) is the Larmor frequency of the proton m the magnetic field. The expression for (Rjj) is an approximation assuming an internally rigid molecule. Figure 8 Effects of spin diffusion. The NOE between two protons (indicated by the solid line) may be altered by the presence of alternative pathways for the magnetization (dashed lines). The size of the NOE can be calculated for a structure from the experimental mixing time, and the complete relaxation matrix, (Ry), which is a function of all mterproton distances d j and functions describing the motion of the protons, y is the gyromagnetic ratio of the proton, ti is the Planck constant, t is the rotational correlation time, and O) is the Larmor frequency of the proton m the magnetic field. The expression for (Rjj) is an approximation assuming an internally rigid molecule.

See pages that mention the term Gyromagnetic ratio : [c.197]    [c.369]    [c.1466]    [c.1475]    [c.1552]    [c.150]    [c.162]    [c.195]    [c.458]    [c.490]    [c.585]    [c.680]    [c.755]    [c.801]    [c.898]    [c.376]    [c.461]    [c.136]   
Encyclopedia of materials characterization (1992) -- [ c.461 ]