Bq , static magnetic field

Fig. 7.2 The principle of an ESR experiment in excited triplet states. C = crystal cos t= high-frequency field N S = magnet Bq = static magnetic field strength UV = optical excitation Ph = phosphorescence.

Chemical shifts of resonances obtained in solution NMR spectra have been routinely used for molecular structure identification and characterization of the organic solutes. In solution, the organic solutes undergo motion in all degrees of freedom including rotation and translation movement that is faster that the time scale of NMR measurement, viz. microseconds. As a result, the observed resonance is at the isotropic chemical shift, which is representative of the molecular structure and electronic environment averaged over all orientations with respect to the Bq (static magnetic field) direction. The relative intensities of the various resonances are usually representative of the relative mole fractions of the respective nuclei in the solution. 

A = hyperfine coupling constant Bq = static magnetic field = microwave magnetic field ... 

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