Problem with simulation of coupled pair spectra

[binet]

I am trying to simulate the powder spectrum of two coupled electrons with a dipolar interaction and either with or without an isotropic interaction (J).
I get exactly the same spectra whether J=0 or J≠0.
Thank you for your help.
Laurent

[Stefan Stoll]

This is a consequence of the fact that the two spins have identical g values, g1 = g2. As soon as you make them non-identical, the isotropic exchange coupling J will have an effect. In general, the regime |g1-g2|<|J| is less intuitive than the regime |g1-g2|>|J|, in which case you get the expected doublet of doublets.