  We consider a three-level quantum system interacting with a bosonic thermal
reservoir. Two energy levels of the system are nearly degenerate but well
separated from the third one. The system-reservoir interaction constant is
larger than the energy difference of the degenerate levels, but it is smaller
than the separation between the latter and the remaining level. We show that
the quasi-degeneracy of energy levels leads to the existence of a manifold of
quasi-stationary states, and the dynamics exhibits two characteristic time
scales. On the first, shorter one, initial states approach the quasi-stationary
manifold. Then, on the much longer second time scale, the final unique
equilibrium is reached.
