d2 Tanabe-Sugano diagram
A Tanabe-Sugano diagram of the spin-allowed and some forbidden transitions for octahedral d2 and tetrahedral d8 complexes is given below.
spin-allowed transitions
(Δ/B' > 13.5)
Solid lines
3A2g(P) ← 3T1g Green
3T1g(F) ← 3T1g Blue
3T2g(F) ← 3T1g Red

spin-forbidden transitions
dotted lines
1A1g(S) ← 3T1g purple
1Eg (G) ← 3T1g Copper
1T1g(G) ← 3T1g Lt green
1A1g(G) ← 3T1g Grey
1T2g(G) ← 3T1g Brown
1Eg (D) ← 3T1g Orange
1T2g(D) ← 3T1g Teal

Select the region of interest (usually between 15-30 Δ /B) then click on the curve to get values. See the instructions for more information.

For the octahedral d2 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 Δ.
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 d8 case, the transitions are expected at much smaller values of Δ/B since Δtet ~ 4/9 Δoct. (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 © 2003-2011 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 25th March 2011.
URL http://wwwchem.uwimona.edu.jm/courses/Tanabe-Sugano/TanSugd2.html