I Microstates of an atom in an energy state

[Sebas4]

I have a question about a sentence in the book Introduction to Thermal Physics (Daniel v. Schroeder).

So in chapter 6, Schroeder talks about an atom isolated. This means its energy is fixed.
The atom is in some state. The energy states of the atom have degenerated. All microstates with that energy the atom has are equally probable.

Now they are talking about a reservoir with a constant temperature. There is an exchange of energy between the reservoir and the atom.
Then Schroeder says that "In this case, the atom would conceivably be found in any of its microstates, but some will be more likely than others, depending on their energies.". I don't get this sentence.

So there is always heat exchange between the atom and the reservoir?
Because if there is no heat exchange between the reservoir and atom, the atom cannot be found in any of its microstates because the energy is fixed.

I hope someone can clarify this sentence.

Thank you in advance.

- Sebas4.

 

[hutchphd]

There is an exchange of energy between the reservoir and the atom.

This means that there must be an interaction between the recevoir and the atom (otherwise it would be invisible to it). Usually this will lift some of the degeneracy for the no longer isolated atom. Perhaps that is his point...I do not know for sure.