An Etymological Dictionary of Astronomy and Astrophysics

A sequence of → permitted transitions in the → ultraviolet from an → excited state (B) of the → molecular hydrogen (H₂) to the electronic → ground state, with ΔE > 11.2 eV, λ < 1108Å (first → band head).
When a hydrogen molecule absorbs such a photon, it undergoes a transition from the ground electronic state to the excited state (B). The following rapid → decay creates an → absorption band in that wavelength range.
See also → Werner band. → Lyman-Werner photon.

See also: → Lyman (Th. Lyman, 1906, Astrophys. J. 23, 181); → band.