Rydberg constant
In spectroscopy, the Rydberg constant, symbol R ∞ {\displaystyle R_{\infty }} for heavy atoms or R H {\displaystyle R_{\text{H}}} for hydrogen, named after the Swedish physicist Johannes Rydberg, is a physical constant relating to the electromagnetic spectra of an atom. The constant first arose as an empirical fitting parameter in the Rydberg formula for the hydrogen spectral series, but Niels Bohr later showed that its value could be calculated from more fundamental constants according to his model of the atom.