MgII
MgII refers to singly ionized magnesium, Mg+, a common ion in many astrophysical and laboratory plasmas. In Mg II the electronic configuration is [Ne]3s1, and the ground term is 2S1/2. The first and second ionization energies are about 7.646 eV and 15.035 eV, respectively. The most prominent spectral feature associated with Mg II is the resonance doublet at 2796.35 Å and 2803.53 Å, produced by transitions from the 3p 2P upper levels to the ground 3s 2S1/2 state. The lines arise from the fine-structure components 2P3/2 → 2S1/2 and 2P1/2 → 2S1/2. The oscillator strengths are approximately f(2796) ≈ 0.612 and f(2803) ≈ 0.305, leading to a 2:1 strength ratio in optically thin gas; in saturated absorbers the observed depths approach parity.
Mg II lines have broad utility in astronomy. The Mg II doublet is a primary tracer of
Magnesium is an alpha-element produced in massive stars and distributed by core-collapse supernovae; Mg II thus