d6 low spin Tanabe-Sugano diagram
A Tanabe-Sugano diagram of some spin-allowed and forbidden transitions for low spin octahedral d6 complexes is given below.
spin-allowed transitions
SOLID LINES
1T2g(I) ← 1A1g Blue
1T1g(I) ← 1A1g Red
spin-forbidden transitions
dotted lines
5Eg (D) ← 1A1g Copper
3T2g(F) ← 1A1g purple
3T1g(H) ← 1A1g Lt green
3T2g(H) ← 1A1g Grey
3T1g(H) ← 1A1g Brown
5T2g(D) ← 1A1g Teal

Select the region of interest (usually between 20-40 Δ /B) then click on the curve to get values. See the instructions for more information.

For the d6 low spin case, the ground term is 1A1g which is plotted along the X-axis. The first spin-allowed transition is to the 1T1g level which is the red line. The second spin-allowed transition is to the 1T2g level (drawn in blue) and the remaining spin allowed transitions are very high in energy, so ignored.

The low-energy spin-forbidden transitions arising from the 5D, 3H and 3F terms are shown as well (teal, orange, gray, light green, copper and purple).

If the lowest spin-allowed energy Peak 1 is at cm-1 and the ratio of the energies (ν2/ν1) is then
to find where this ratio falls on the Tanabe-Sugano diagram and get the predicted value of B' and the energy of the transitions.
Initial output is:

From this a JCAMP-DX file can be created suitable for plotting with MDL CHIME
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Copyright © 2004 by Robert John Lancashire, all rights reserved.

Created and maintained by Prof. Robert J. Lancashire,
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.
Created Dec 2003. Links checked and/or last modified 3rd August 2004.
URL http://wwwchem.uwimona.edu.jm/courses/Tanabe-Sugano/TanSugd6ls.html