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Is photon emission possible without electrons changing energy levels?

  1. Feb 6, 2012 #1
    Does molecular vibrational transition and consequent emission of infrared radiation involve electrons changing energy level? In wikipedia, about vibronic transitions it says "Most processes leading to the absorption and emission of visible light, are due to vibronic transitions. This may be contrasted to pure electronic transitions which occur in atoms and lead to sharp monochromatic lines (e.g. in a sodium vapor lamp) or pure vibrational transitions which only absorb or emit infrared light.". Does this mean infrared radiation is emitted without electrons playing a direct part? What about changing in molecular rotational energies? Also, I understand reflection is not a radiation absorption-emission phenomena, so can you explain what actually happens to the photons? Same thing for radiation scattering.
     
  2. jcsd
  3. Feb 6, 2012 #2
    The photons emitted don't have to be real photons, they can be virtual photons. When you push on an object, you are pushing on the atoms themselves via the repulsion between your atoms and those atoms, and this happens with the exchange of virtual photons that carry the EM force. Otherwise, if charged particles "accelerate", not just move, but actually change velocity, then according to my understanding they will emit or of have to of absorbed a photon. Vibration is from kinetic energy, kinetic energy in vibrations causes atoms to accelerate, atoms will accelerate and release/gain various frequencies (though most often on Earth its infrared) photons according to how much they accelerate.
     
  4. Feb 9, 2012 #3
    Thank you for your answer, but I don`t think you addressed the issues I questioned about.
     
  5. Feb 10, 2012 #4

    ZapperZ

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    First, to just address your "topic", just in case you think that ALL light are emitted by electron transition, the answer is no. Synchrotron light sources generate light simply by accelerating electrons, or making them wiggle up and down.

    Secondly, when you have vibrational states, these involve ADDITIONAL states that are not present in an isolated atom. So yes, these involve electronic transition as well. But the states are often every close together (depends on the complexity of the molecule) and very often, you do not see any discrete lines (see your ordinary light bulb).

    Zz.
     
  6. Feb 10, 2012 #5
    Just to add to that. Photons couple to charge. So they will involve some interaction with a charged particle.

    This can correspond to an electron in atomic transition of a given 'energy' or an electron/charged particle being accelerated by some external field. Whether the energy you give the photon is from the internal structure of an atom or an external field doesn't really matter.

    Hope this helps.
     
  7. Feb 10, 2012 #6
    ZapperZ, thank you for your answer! just to make sure I understood what you meant , you say that vibrational or rotational molecular transitions produce photons because they also involve electrons changing energy levels? I suppose that invalidates the direct interpretation of the wikipedia statement. That´s your saying?

    RGauld, also thank you for answering! If I understand your statement photons are always related to electrons, so infrared photons produced by vibrational energy levels changing in a molecule, as an example, are due to the fact that in those transitions, electrons must also be changing their proximity to atomic nucleolus in the molecule, and therefore they are directly responsible by photon emission. Is this what you meant?
     
  8. Feb 11, 2012 #7
    Yeah. Of course it could be an electron or a positron or anything charged.

    In that case yes indeed. The atom changes energy level and spin and emitts a photon :)
     
  9. Feb 11, 2012 #8
    Actually, no. A hydrogen atom in the ground state in an electric field can have its orbital distorted in relation to the proton. This leads to radiation and absorption without requiring electronic transitions.
     
  10. Feb 11, 2012 #9
    But isnt that just an example of subjecting the atom to an external field. So it is another way of exciting the system ie putting energy in. Like what is mentioned above in the post.

    Thanks for the reply.
     
  11. Feb 19, 2012 #10
    ZapperZ, thank you for your answer! just to make sure I understood what you meant , you say that vibrational or rotational molecular transitions produce photons because they also involve electrons changing energy levels? I suppose that invalidates the direct interpretation of the wikipedia statement. That´s your saying?
     
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