Do Free Electrons Emit or Absorb Photons?

[CosmicVoyager]

Greetings,

I know that when an electron in an atom emits or absorbs a photon, what changes is the electrons orbit.

What about free electrons? If an electrons moving freely through space emits or absorbs an electron, what changes about the electron? And what determines what frequency photons correspond to free electron?

Thanks

 

[SpectraCat]

EM radiation is emitted from oscillating charges. If you have free electrons, they will emit at whatever frequency they are driven to oscillate at. This is the principle behind a free-electron laser.

http://en.wikipedia.org/wiki/Free-electron_laser

 

[CosmicVoyager]

So electrons can't travel in a straight line out in the vacuum of space?

If they can, can they absorb photons?

If so, what determines the frequency they can absorb?

 

[SpectraCat]

So electrons can't travel in a straight line out in the vacuum of space?

If they can, can they absorb photons?

If so, what determines the frequency they can absorb?

Just invert my previous answer ... EM radiation is an oscillating electric field (at least in the classical description) ... classically, the negatively charged free electron would try to follow the motion of the field. Quantum mechanically, we would expect a non-zero probability that a free-electron can absorb EM-radiation at (almost?) any frequency. What's more, electrons can scatter photons inelastically in a process called Compton scattering (http://en.wikipedia.org/wiki/Compton_scattering).

Having said all of that, the correct way to describe this is by using quantized fields. Specifically, quantum electrodynamics (QED) deals with the interactions of EM-radiation and matter on the quantum level. I am less familiar with the details of QED, but I believe it is consistent with what I said above. Certainly one can draw a Feyman diagram representing absorption or emission of a photon from a free-electron.

 

[CosmicVoyager]

Can an electron that is moving freely in the vacuum of space and not interacting with anything spontaneously emit a photon?

If so, does that cause the electron to slow down because it has lost energy?

Are faster moving electrons capable of emitting higher frequency photons?

 

[SpectraCat]

An electron can only emit when it is under acceleration, therefore if it is a "free" electron, and is not interacting with anything, it cannot be under acceleration, and thus cannot emit.

 

[Lapidus]

Greetings,

I know that when an electron in an atom emits or absorbs a photon, what changes is the electrons orbit.

What about free electrons? If an electrons moving freely through space emits or absorbs an electron, what changes about the electron? And what determines what frequency photons correspond to free electron?

Thanks

Check Compton scattering
http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/comptint.html