Relaxation in the rotating frame

The locking rf fields can have a range of amplitudes. Thus a range of motional frequencies can be investigated by simply changing the amplitude of Hjj or Hq. 

The process of relaxation of M to a value proportional to the applied rf fields in the rotating frame is called spin-lattice relaxation in the rotating frame. The mechanisms available for this form of relaxation are entirely analogous to those available for simple spin-lattice relaxation as described above. Similarly, rotating frame relaxation is characterized by a time constant analogous to Tj, and is called Tjp, or the spin-lattice relaxation time in the rotating frame. Typically, Tj p values obtained from protons in solid samples are not of much use, since communication between the abundant protons tends to average the relaxation process, so that individual proton relaxation mechanisms cannot be observed. For however, 

As noted in the papers by Schaefer and coworkers and by Lyerla and coworkers, Tj p data may be complicated by the fact that mechanisms other than spin-lattice interactions (namely spin-spin relaxation) are possible which don t map motional characteristics. In the case of polystyrene, Schaefer and coworkers conclude that the spin-spin contributions are negligible, whereas Lyerla and coworkers find that the levels of spin-spin and spin-lattice contributions for isotatic polypropylene and atatic polymethyl methacrylate were temperature dependent. 

All the above techniques can be combined with any of the acquisition methods discussed earlier (FID or single point detection). This allows the possibility of a full two-dimensional analysis of the data, which has been suggested by other authors but not carried out in practice [5]. 

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Deverell C, Morgan R E and Strange J FI 1970 Studies of ohemioal exohange by nuolear magnetio relaxation in the rotating frame Mol. Phys. 18 553-9... 

Bull, T. E. Relaxation in the rotating frame in liquids. Prog. Nucl. Magn. Reson. Spectrosc. 1992, 24. 

The cross-relaxation in the rotating frame (dashed lines in fig. 1) mono-tonically increases with correlation time. For looTc < 0.382 two crossrelaxation rates, cr" and (T have similar dependence on correlation time, and at the limit when loqTc —> 0, the extreme narrowing limit, their ratio... 

Relaxation in the rotating frame is determined by the strength of the spin-locking field Br Therefore, Tt times are sensitive to the intermediate frequencies co1 = yBt, in the kHz region 9) ... 

The 2D ROE or ROESY experiment is an experiment to measure cross-relaxation in the rotating frame (Fig. 8.2B). After an initial 90° pulse and the variable evolution period t, a low power or soft spin-lock sequence (SL) is applied for a time during which magnetization transfer in the rotating frame occurs due to cross relaxation. Since scalar connectivities can also develop during spin lock, as... 

Cross-link density and parameters relating to the network structure can be measured by NMR by analysis of the transverse relaxation decay (cf. Section 1.3) and the longitudinal relaxation in the rotating frame [67]. Combined with spatial resolution, the model-based analysis of relaxation yields maps of cross-link density and related parameters [68]. Often the statistical distribution of relaxation parameters over all pixels provides a reduced data set with sufficient information for sample characterization and discrimination [68]. 

The combination of HOHAHA transfer with cross-relaxation in the rotating frame leads to TOCSY-ROESY (TORO) or ROESY-TOCSY (ROTO) experiments (Kessler et al., 1988a Williamson et al., 1992). Two-dimensional hetero-TOCSY-NOESY experiments (Kellogg et al., 1992 Kellogg and Schweitzer, 1993), which combine heteronuclear Hartmann-Hahn transfer with a homonuclear NOESY mixing step, have been used for a P-driven assignment strategy of RNA and DNA spectra. 

Crystalline a-D-galacturonic acid monohydrate has been studied by C CPMAS NMR and X-ray crystallography. The molecular dynamics have been investigated by evaluating C spin-lattice relaxation in the rotating frame (Tip) and CSA properties of each carbon. It has been found that only limited molecular motions can be detected in the low frequency (<10 Hz) range by Tip( C) measurements and changes of CSA properties as a function of temperature. 

Similar to transverse relaxation longitudinal relaxation in the rotating frame is also sensitive to slow molecular motion (cf. Fig. 7.1.3) and is thus a good probe for elastomer... 

In summary, then, all relaxation processes can ultimately be described as some linear combination of spectral density functions of the form shown in Eq. (11). We have here only considered explicitly the case of longitudinal or spin lattice relaxation in the laboratory frame (the so-called spin-lattice relaxation in the rotating frame being a different process), but a similar case can be made for transverse relaxation, relaxation processes in the rotating frame and crossrelaxation processes. The spectral densities involved in each case are J f( Mo> ) where co is the frequency of rotating frame transformation required to remove the stationary part of the total spin Hamiltonian in each case. This will be the Larmor frequency, co0, for any relaxation process taking place in the laboratory frame. For relaxation processes taking place... 

A cured epoxy synthesised from a mixture of the diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylenediamine was studied by NMR spectroscopy including multiple pulse techniques and spin-lattice relaxation in the rotating frame. Tip. The study [28] focused on the water distribution based upon possible variation in the cross-link density measured by spin diffusion. From the analysis involving a combination of Tip and multiple... 

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