# Can unbound electrons jump energy levels?

If an unbound electron (or indeed any charged particle) is moving through free space, is there a probability that it can spontaneously change energy by emitting a photon, or does this require the presence of an external potential $A_4$.

The important point is that the process is spontaneous, like jumping energy levels in an atom.

I'm pretty sure this violates some conservation law but I just want to check.

-