  I revisit the problem of the interaction between two dissimilar atoms with
one atom in an excited state, recently addressed by the authors of Refs.[1-3],
and for which precedent approaches have given conflicting results. In the first
place, I discuss to what extent Refs.[1], [2] and [3] provide equivalent
results. I show that the phase-shift rate of the two-atom wave function
computed in Ref.[1], the van der Waals potential of the excited atom in Ref.[2]
and the level shift of the excited atom in Ref.[3] possess equivalent
expressions in the quasistationary approximation. In addition, I show that the
level shift of the ground state atom computed in Ref.[3] is equivalent to its
van der Waals potential. A diagrammatic representation of all those quantities
is provided. The equivalences among them are however not generic. In
particular, it is found that for the case of the interaction between two
identical atoms excited, the phase-shift rate and the van der Waals potentials
differ. Concerning the conflicting results of previous approaches in regards to
the spatial oscillation of the interactions, I conclude in agreement with
Refs.[1,3] that they refer to different physical quantities. The impacts of
free-space dissipation and finite excitation rates on the dynamics of the
potentials are analyzed. In contrast to Ref.[3], the oscillatory versus
monotonic spatial forms of the potentials of each atom are found not to be
related to the reversible versus irreversible nature of the excitation transfer
involved.
