d7 Tanabe-Sugano diagram
A Tanabe-Sugano diagram of the spin-allowed and some forbidden transitions for high spin octahedral d7 complexes is given below.
spin-allowed transitions (Δ/B' > 13.5)
3A2g(P) ← 3T1g Green
3T1g(F) ← 3T1g Blue
3T2g(F) ← 3T1g Red
spin-forbidden transitions
dotted lines
2T1g(P) ← 3T1g Yellow
2T2g(D) ← 3T1g Dk green
2Eg(H) ← 3T1g Purple
2T1g(H) ← 3T1g Copper
2T2g(H) ← 3T1g Lt green
2A1g(G) ← 3T1g Grey
2T1g(H) ← 3T1g Brown
2T1g(G) ← 3T1g Orange
2Eg (G) ← 3T1g Teal

Select the region of interest (usually between 0-20 Δ /B) then click on the curve to get values. See the instructions for more information.

For the d7 case, the ground term is 3T1g which is plotted along the X-axis. The first spin-allowed transition is to the 3T2g level which is the red line. The other spin-allowed transitions are to the 3A2g level (drawn in green) and to 3T1g (P) level (drawn in blue) the order depending on the size of D.

The low-energy spin-forbidden transitions arising from the 1D, 1G and 1S terms are shown as well (teal, orange, gold, gray, light green, dark green and copper).

For the tetrahedral d7 case, the transitions are expected at much smaller values of D/B since Dtet ~ 4/9 Doct. (The subscript g's should be dropped as well.)

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/TanSugd7.html