Two-Spin Operators -coupling Evolution and Antiphase Coherence

5 TWO-SPIN OPERATORS /-COUPLING EVOLUTION AND ANTIPHASE COHERENCE 

For a system with two kinds of nuclei, the symbols I and S are used to represent the two nuclei. For example, in a system, the lH is usually represented as I and the 13C as 

The six simple spin states I, I-y, Iz and S, S-y, Sz can be represented, but we can also form products of these spin states to represent situations which cannot be described by the vector model. This is where the product of product operator comes from. Consider first the product of one nucleus in the x -y plane with another nucleus on the z axis  

21ySz I (1H) magnetization in the x -y plane, antiphase with respect to the z orien- 

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