noun

• An equation giving the wave numbers of the spectral lines of hydrogen or hydrogen-like atoms, especially of a hypothetical atom having a nucleus of infinite mass.

  The Rydberg formula for a hydrogen-like atom is 1/λ = RZ 2(1/n 2 − 1/m 2), where λ is the wavelength of the light, R is the Rydberg constant, Z is the atomic number of the atom, and n and m are whole numbers, with m > n.