Field-cycling motional frequencies

Fluctuations in the orientation of the director are better investigated by field cycling experiments that allow frequency-dependent Tj measurements to be performed over a range from 100 Hz to 10 MHz. H and H spin relaxation studies have been carried out for numerous nematic and smectic liquid crystals to investigate the frequency dependence of director fluctuations, not accessible by experiments run on standard NMR spectrometers. It has been found that this motion is clearly observable by the relaxation... 

Fig. 5. Schematic representation of the experimental temperature/frequency window conveniently accessible by field-cycling NMR relaxometry in combination with conventional high-field techniques. It specifically addresses the chain-mode regime of typical polymers, whereas local segment fluctuations and center-of-mass motions can only be probed at low temperatures/high frequencies and high temperatures/low fi-equencies/low molecular weights combinations, respectively...

To qualitatively understand the mechanism of impulsive Raman excitation, we apply the above-mentioned cycle average condition to the harmonic oscillator model for a Raman active mode I of which the reduced mass and vibrational frequency are ft/ and an, respectively. The applied pulse is assumed to be rectangular, and the duration is Tp./(f) is constant, that is,/(f) = / for the pulse duration. From Eqs. (7.7) and (7.8), we can derive the classical equation of motion for Qi. The field-induced... 

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