# Isogenous series

Isogenous is a term occasionally used in spectroscopy that denotes when two or more spectroscopic series of transition from a common state. The word was first used in this context in T.J. Stone & R.F. Barrow Laser excited fluorescence spectra of gaseous ${\displaystyle Te_{2}}$, Canadian Journal of Physics. Vol. 53, p. 1976, October 1975. In this case, an excited state of gaseous ${\displaystyle Te_{2}}$ was pumped by an Argon ion laser; the excited state then relaxed to two closely separated low lying states giving two series of emission lines with a common origin.