## rotational constants

https://doi.org/10.1351/goldbook.R05409
Coefficients of quantum numbers in the rotational @T06272@ expression and inversely proportional to the @P04848@. Symbols: $$A$$, $$B$$, $$C$$. $$\overset{˜}{A}=\frac{h}{8\ \pi ^{2}\ c\ I_{\text{A}}}$$ (dimension wavenumber), $$A=\frac{h}{8\ \pi ^{2}\ I_{\text{A}}}$$ (dimension frequency) where $$h$$ is the @P04685@ and $$c$$ the speed of light in vacuum.
Source:
Green Book, 2nd ed., p. 23 [Terms] [Book]