d4 low spin Tanabe-Sugano diagram
A Tanabe-Sugano diagram of some spin-allowed and forbidden transitions for low spin octahedral d4 complexes is given below.
spin-allowed transitions
3Eg(G) ← 3T1g Purple
3A2g(F) ← 3T1g Copper
3A1g(G) ← 3T1g Cyan
3T2g(H) ← 3T1g Green
3T1g(H) ← 3T1g Blue
3Eg(H) ← 3T1g Red
spin-forbidden transitions
dotted lines
5T2g(D) ← 3T1g yellow
1A1g(S) ← 3T1g Lt green
1Eg(D) ← 3T1g Grey
1T2g(D) ← 3T1g Brown
5Eg(D) ← 3T1g Teal

Select the region of interest (usually between 30-50 Δ /B) then click on the curve to get values. See the instructions for more information.

For the d4 low spin case, the ground term is 3T1g which is plotted along the X-axis. The first spin-allowed transition is to the 3Eg level which is the red line. The second spin-allowed transition is to the 3T1g level (drawn in blue) and the remaining spin allowed transitions arise from the 3G and 3F terms.

The low-energy spin-forbidden transitions arising from the 5D, 1D and 1S terms are shown as well (teal, orange, gray, light green, copper and purple). Note that the lowest lines are likely to be in the NIR region.

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/TanSugd4ls.html