Mg I Grotrian diagram for the structure of 85-level models. Fine structure is included up to level 7i ¹I (level 54, 59 430.517 cm⁻¹) (not distinguishable in the figure). The first 54 energy levels are fully represented. Superlevels (between nl = 9s and 20p) are shown with their average energy as a solid green line, very close to the continuum (which occurs at 61 671.05 cm⁻¹). Level 3p² (68 275 cm⁻¹) is represented as a solid blue line. In cyan dashed lines, the 210 transitions included in the spectrum are shown.