Product operators and coherence transfer in multiple‐pulse NMR experiments

A practical introduction to coherence and coherence transfer pathways in NMR is provided using the density matrix and product‐operator formalisms. The concept of coherence in NMR is first introduced using the density matrix formalism. Pictorial and quantitative representations of coherence are provided using product operators in the Cartesian basis. A simple transformation from the Cartesian basis to a spherical basis is used to follow coherence order during multiple‐pulse experiments with coherence transfer pathways. The rules are introduced for designing phase cycles to eliminate unwanted coherences and pathways. An appendix contains a computer program written in Mathematica for performing product‐operator calculations interactively.