Question 11.4 (in my version at least) has a confusing sub section.
'If the atom is diatomic, derive a condition on the quantities eta_A - eta_B as well as t_AA and t_BB.'
For a start, what does 'If the atom is diatomic' mean? I think this must be a typing error.
Secondly, how does one derive the condition? I am loth to solve the schroedinger eq in gory detail, this not being an atomic and lasers course question. Even if I did that, I would have only found energy levels and exchange integrals, left in terms of model parameters. Not so helpful.