What happens as a result of the interaction of cosmic electromagnetic radiation with particles of the interstellar medium

What happens as a result of the interaction of cosmic electromagnetic radiation with particles of the interstellar medium: an electron, an atom, a molecule?

When an electromagnetic wave interacts with an electron, scattering of photons occurs, since absorption and emission of a photon cannot occur during such an interaction. Freely moving atoms and molecules can absorb and emit.

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