d5 low spin Tanabe-Sugano diagram
A Tanabe-Sugano diagram of some spin-allowed and forbidden transitions for low spin octahedral d5 complexes is given below.
spin-allowed transitions
SOLID LINES
2A1g(I) ← 2T2g Purple
2T2g(F) ← 2T2g Cyan
2Eg(I)   ← 2T2g Green
2T2g(I) ← 2T2g Blue
2A2g(I) ← 2T2g Red
spin-forbidden transitions
dotted lines
4A1g(G) ← 2T2g Copper
4T1g(E) ← 2T2g Lt green
4T2g(G) ← 2T2g Grey
4T1g(G) ← 2T2g Orange
6A1g(S) ← 2T2g Teal

Select the region of interest (usually between 30-55 Δ /B') then click on the curve to get values. You can then use the ratio obtained to submit via the input field below. See the instructions for more information.

For the d5 low spin case, the ground term is 2T2g(I) which is plotted along the X-axis. The first spin-allowed transition is to the 2A2g(I) which is very close in energy to the 2T1g(I) level so only the 2A2g(I) is shown (the red line). The third spin-allowed transition is to the 2T2g(I) level (drawn in blue). The fourth 2Eg(I) (green), fifth 2T2g(F) (cyan) and sixth 2A1g(I) (purple) lines are shown as well but higher energy terms are ignored.

Some low-energy spin-forbidden transitions arising from the 6A, 4G and 4E terms are shown as well (teal, orange, grey, light green and copper).

If the lowest spin-allowed energy Peak 1 is at cm-1 and the ratio of the energies (ν 2T2g/ν 2A2g) 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/TanSugd5ls.html