Spin probe orientation distribution

Figure 3. ESR lineshapes of spin probes in frozen (a) and mobile (b) hosts, (s The magnetic dipoles m of immobile spin probes in a frozen liquid have different u>o values due to their different orientations with respect to Bo, thus resulting in a broad line with width Arno (black line), usually referred to as rigid-limit or pwder lineshape. (b) If the spin probe undergoes rotation (sketched as instantaneous clockwise jumps at random times), ft>o fluctuates. When the rotational rate 1/r is larger than the width of the coo distribution Acoo, the different precession frequencies become indistinguishable and an average value is seen, that is, the ESR lineshape coalesces (motional narrowing) [4,14]. Adapted from Ref. [26].

We first consider the spin probes as immobile in a frozen host with isotropic distribution of their orientations. In that case the energy levels of the spin... 

Owing to the orientation distribution of the spin probes, and then of n, distribution resulting in a broad absorption line when sensitive signal detection. The field-swept derivative pattern of the ESR lineshape in the absence of spin probe motion (powder lineshape) shows sharp details that allow one to measure the principal values of the Zeeman g tensor (Fig. 5, top right). 

Electron spin Resonance Absorption of radiation giving rise to transitions between opposite spin orientations of unpaired electrons in a magnetic field P Detection and estimation of free radiceds emd diagnosis of their structure and electron distribution of metalloproteins. For other biomacromolecules, probes are needed. 

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