Title: rotational constants
Long Title: IUPAC Gold Book - rotational constants
DOI: 10.1351/goldbook.R05409
Status: current

Definition
Coefficients of quantum numbers in the rotational term expression and inversely proportional to the principal moments of inertia. Symbols: \(A\), \(B\), \(C\). \(\overset{˜}{A}=\frac{h}{8\ \pi ^{2}\ c\ I_{\rm{A}}}\) (dimension wavenumber), \(A=\frac{h}{8\ \pi ^{2}\ I_{\rm{A}}}\) (dimension frequency) where \(h\) is the Planck constant and \(c\) the speed of light in vacuum.

Related Terms
- Planck constant: https://goldbook.iupac.org//terms/view/P04685
- principal moments of inertia: https://goldbook.iupac.org//terms/view/P04848
- term: https://goldbook.iupac.org//terms/view/T06272

Source
- Green Book, 2nd ed., p. 23 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/R05409/html
- json: https://goldbook.iupac.org/terms/view/R05409/json
- xml: https://goldbook.iupac.org/terms/view/R05409/xml

Citation: Citation: 'rotational constants' 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.R05409
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Accessed: 2026-06-20T02:19:23+00:00