ESR Spectroscopy of ARs

In solutions with low viscosity, ARs are rapidly rotated with total averaging g -and T -tensors. Therefore, ESR spectra of ARs in solutions are characterised by a triplet signal with the component intensity ratio of 1 1 1 owing to interaction of unpaired electrons with the nucleus having 1=1. This triplet splits because of interactions with magnetic nuclei in a and P positions. Isotropic HFI constants dependent on AR structure are given below [9]  

The equations (Equation 2.10) and (Equation 2.11) are valid for = 5 xl0 to 5 xl0 s. The correlation time is connected with the radius of rotating molecules and viscosity of the solvent t by the Stokes equation  

For determining x in the range of slow movements ( T 5 x 10 s), the dependence of X on shift of the high-held line A relative to its position in the ESR spectrum can be used [11]  

Using the equation (Equation 2.13) one can calculate x in the range of 5 x 10 to 5 x 1 s, and use these values in studies of the rotational diffusion of macromolecules. 

The correlation time can be expressed as a function of the parameter S = where A is half of distance between extremes of the outside lines of the triplet ESR spectrum and A is the same value in conditions of extremely slow movements of ARs [12]  

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