Nuclear hyperfine shift and relaxation

If the interaction energy fluctuates, then nuclear relaxation enhancements occur. Such relaxation enhancements are proportional to the average squared interaction energy 

Upon rotation the average electron induced magnetic moment causes nuclear relaxation. This is called Curie relaxation (see Section 3.6). However, the full electron magnetic moment causes nuclear relaxation through dipolar and contact mechanisms by jumping over the various Zeeman levels. The electron jumps over the Zeeman levels with rates equal to the electronic R or R2 values and such jumps give also rise to nuclear relaxation. 

The present Chapter deals with the hyperfine shifts which are only due to the average electron induced magnetic moment and therefore are related to (Sz). Chapter 3 will deal with nuclear hyperfine relaxation which, as discussed above, depends on both average electron induced magnetic moment (Curie relaxation) and on the full electron magnetic moment (dipolar and contact relaxation). 

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