Spin-lattice relaxation in the rotating frame

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. 

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... 

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 T, and is called Tip, or the spin-lattice relaxation time in the rotating frame. Typically, Tip 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 C, however,... 

Other relaxation processes mentioned in this book are those characterized by Tj and T. The former is called spin-lattice relaxation in the rotating frame and is discussed in IV.C. while the latter is called dipolar spin-lattice relaxation and is discussed in IV. B. 

We can understand spin-lattice relaxation in the rotating frame by first understanding the experiment to observe this process. It is done by the following technique or some variation of it. The sample is placed in a large applied field Hq... 

Studies of P spin-lattice relaxation in the rotating frame in... 

Fig. 29. Filter-weighted and spin-lattice relaxation in the rotating frame Tip of an elastomer composite of SBR and natural rubber cut from the tread of a car tire, (a) A stack of one-dimensional images with variable duration tf of the spin-lock radio-frequency magnetic field, (b) A Tip parameter map obtained from the decay shown in (a). Reproduced from Ref 143, with permission from Wiley.

Spin-lattice relaxation in the rotation frame This rrfers to magnetisation along the radiofrequency magnetic field B, is characterised by a time T requires motion at a frequency related to the strength of B (i.e. tens of kHz) and is somewhat mote difficrrlt to average by spin diifitsion than T,. 

Frequently polymer heterogeneity can be monitored by measurement of Figure 4.13 shows experimental and computer-fitted plots [17] of spin-lattice relaxation in the rotating frame for a sample of PVC. The decay curve can be satisfactorily fitted by two exponentials, giving 72% with — 8.8 ms and 28%... 

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