A pair of forbidden spectral lines of the same atom arising from
a common upper excitation level, for example [O III] λ 5007 and
[O III] λ 4959, [N II] λ 6584 and [N II] λ 6548, and [S II] λ 6717,
[S II] λ 6731.
From O.Fr. doublet, from → double + -et diminutive suffix.
Dotâyé, from dotâ→ double + -(y)é nuance suffix.
[O III] doublet
dotâye-ye [O III]
Fr.: doublet [O III]
The two → forbidden lines with → transitions from the upper → energy level 1D2 of the doubly ionized oxygen atom. They occur in the green part of the → visible spectrum and are called → nebular lines. They are λ5006.8 1D2-3P2 and λ4958.9 1D2-3P1. Theoretical values for the [O III] 5007/4959 line-intensity ratio is 3.01 (Storey and Zeippen, 2000, MNRAS 312, 813).
[O III], spectroscopic notation of the ion O++; → doublet.