The magnesium UV triplet in the solar spectrum
The Fraunhofer b-band triplet in the solar spectrum is stronger than might be expected from a non-resonance (subordinate) line. In the energy level (Grotrian) diagram in the top panel above (US Department of Commerce, National Bureau of Standards, NSRDS-NBS 23, "Partial Grotrian Diagrams of Astrophysical Interest", p16), the lower level of the b-band triplet absorption is seen to be 3p 3P0 which has no permitted transition to the 1S ground level.
The spectrum below shows, marked in green, the analogous triplet absorption in the ultraviolet, 3p 3P0 - 3d 3D, at 3838.3, 3832.3 and 3829.4 which is also strong.
For these transitions, the 3p 3P0 level becomes a pseudo-ground state.
I have now found and posted the plots of all the Mg I lines in the Grotrian diagram that are within the HARPS spectral range. The only one not to show is the 4081.83Å intersystem line.
The magnesium UV triplet in the solar spectrum
The Fraunhofer b-band triplet in the solar spectrum is stronger than might be expected from a non-resonance (subordinate) line. In the energy level (Grotrian) diagram in the top panel above (US Department of Commerce, National Bureau of Standards, NSRDS-NBS 23, "Partial Grotrian Diagrams of Astrophysical Interest", p16), the lower level of the b-band triplet absorption is seen to be 3p 3P0 which has no permitted transition to the 1S ground level.
The spectrum below shows, marked in green, the analogous triplet absorption in the ultraviolet, 3p 3P0 - 3d 3D, at 3838.3, 3832.3 and 3829.4 which is also strong.
For these transitions, the 3p 3P0 level becomes a pseudo-ground state.
I have now found and posted the plots of all the Mg I lines in the Grotrian diagram that are within the HARPS spectral range. The only one not to show is the 4081.83Å intersystem line.