Looping transitions

[sc262]

I am trying to simulate different S = 3/2 chromium(III) complexes formed in situ. Based on different D and E values, I often get this notification:

** Looping transitions found. Artifacts at coalescence points possible.

First of all, I am not familiar with this terminology. Are these similar to turning points? can you provide some reference where I can find information about it.
Secondly, the EPR spectrum generated is much complicated at X-band. is there a way to identify which of these would be the looping transition in simulation?

Thanks!

[Stefan Stoll]

You can see looping transitions when you have two energy levels, say n and m, whose energy difference doesn't grow monotonically with the magnetic field. In that case, you can have more than one field values where resonance can occur. Typically, if one plots all resonance fields against the orientation angle of the system (theta), then these transitions appear as loops.