Rydberg constant

In spectroscopy, the Rydberg constant is a physical constant relating to the electromagnetic spectra of an atom. Its symbol is formula_1 for heavy atoms or formula_2 for hydrogen. The constant is named after the Swedish physicist Johannes Rydberg. The constant first arose as an empirical fitting parameter in the Rydberg formula for the hydrogen spectral series. Niels Bohr later showed that its value could be calculated from more fundamental constants via his Bohr model. , formula_1 and electron spin "g"-factor are the most accurately measured physical constants.
The constant is expressed for either hydrogen as formula_2, or at the limit of infinite nuclear mass as formula_1. In either case, the constant is used to express the limiting value of the highest wavenumber (inverse wavelength) of any photon that can be emitted from an atom, or, alternatively, the wavenumber of the lowest-energy photon capable of ionizing an atom from its ground state. The hydrogen spectral series can be expressed simply in terms of the Rydberg constant for hydrogen formula_2 and the Rydberg formula.
In atomic physics, Rydberg unit of energy, symbol Ry, corresponds to the energy of the photon whose wavenumber is the Rydberg constant, i.e. the ionization energy of the hydrogen atom.