Title: spin projection
Long Title: IUPAC Gold Book - spin projection
DOI: 10.1351/goldbook.ST07106
Status: current

Definition
A component, \(M_{S}\), of the angular spin moment \(S\) along an arbitrary axis (usually chosen as the z-direction). \(M_{S}\) can take the values between \(-S\) and \(S\): \(-S\), \(-S + 1\),..., \(S- 1\), \(S\). The term is also used to denote an operation (spin-symmetry projection) allowing one to eliminate spin contamination in the cases where wavefunctions are not eigenfunctions of the operator \(S^{2}\).

Related Term
- spin contamination: https://goldbook.iupac.org//terms/view/ST07103

Source
- PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1963 (https://doi.org/10.1351/pac199971101919)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/ST07106/html
- json: https://goldbook.iupac.org/terms/view/ST07106/json
- xml: https://goldbook.iupac.org/terms/view/ST07106/xml

Citation: Citation: 'spin projection' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.ST07106
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Accessed: 2026-06-20T23:09:32+00:00