[Winga]

e.g. Octahedral Complex

Is the transition energy different from ligand field strength (10Dq or Delta o)?

The energy gap between t2g and eg is the ligand field strength in terms of energy, 10Dq, right?
So, the energy (E) for t2g to eg transition is the same as the energy gap, 10Dq?

But my professor said they are different, why?

[Major Werner]

the answer to that is yes and no. in transition metals, the mixing and coupling of orbitals gives rise to term symbols which are representations of the energy somewhat like the orbitals. for example a d1 system will give rise to a 2D Term which will split under Oh field to give T2g and Eg. thus the transition 10Dq will be same as that from T2g to Eg. however for a d2 system. it will give rise to to ground terms 3F and 3P. the 3F will split under Oh field to give T1g(f) T2g and A2g. so there are three transitions here, from the ground level, T1g(F) to the other levels. thus making 10Dq more complicated and not necessarily a measure of the splitting betewwen the eg and t2g orbitals.