The Lyman series is the set of emission lines (Lyman lines) from atomic hydrogen gas, due to electrons descending from an electron shell number n greater than 1 down to n = 1, or the analogous absorption lines when absorbed electromagnetic radiation makes electrons do the opposite. It is one of the hydrogen line series, such as the Balmer series and is named after Theodore Lyman. The lines fall within extreme ultraviolet (EUV) and cannot be observed from the ground unless considerably redshifted. Lines:
Formula for the wavelengths:
1/wavelength = RH ( 1 - 1/n² )
Photons with wavelength at or shorter than the Lyman limit can ionize any hydrogen atom, and are termed Lyman continuum photons or LyC photons. Such photons are likely to ionize any neutral hydrogen in clouds they pass through, regardless of whether the hydrogen is excited. Cases where photons, e.g., from a galaxy, avoid such absorption (Lyman continuum escape) are of research interest.
Analogous series to the hydrogen Lyman and Balmer (etc.) series, occur in any atom or ion in possession of only one electron, which use the same formula with a different Rydberg constant:
deuterium Rydberg constant, RD = 1.09707417 × 107 helium-4 Rydberg constant, R4He = 1.09722267 × 107
The series names are sometimes used for these as well, e.g., deuterium Lyman series, HE-II Lyman series, deuterium Balmer series, HE-II Balmer series, etc.