Can electrons absorb a photon?

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    Electrons Photon
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Discussion Overview

The discussion centers around the question of whether electrons can absorb photons, exploring the nature of light and its interaction with electrons and atoms. Participants examine concepts related to reflection, absorption, and the size of photons in relation to electrons, with a focus on theoretical and conceptual understanding.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that electrons absorb photons and move to a higher energy state, while others clarify that isolated electrons cannot absorb photons without context, such as being part of an atom.
  • One participant questions how electrons can absorb light beams that are much larger than them, prompting further discussion on the nature of light and photons.
  • There is a distinction made between scattering and reflecting light, with some arguing that individual electrons scatter light rather than reflect it.
  • A participant expresses skepticism about the current model of the atom and shares their confusion regarding the absorption process, likening photons to a malleable substance.
  • Another participant emphasizes that the size of a photon is not relevant to its interaction with electrons, focusing instead on energy matching.
  • Some participants express frustration over the clarity of sources and the understanding of concepts, indicating a need for better explanations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of electron-photon interactions, with multiple competing views presented regarding absorption, reflection, and the implications of size and energy. The discussion remains unresolved with ongoing questions and clarifications.

Contextual Notes

There are limitations in the understanding of the absorption process, the definitions of reflection versus scattering, and the implications of size in the context of particle interactions. Some statements made by participants reflect misunderstandings or misinterpretations of established concepts.

Who May Find This Useful

This discussion may be useful for high school students or individuals interested in foundational concepts of quantum mechanics, particularly those exploring the interactions between light and matter.

  • #61
Mister T said:
The potential energy is a property of the atom, not a property of anyone single component of the atom.
This is an important point that applies for potential energy in general. We sometimes speak as though it is localized to one part of a system, but generally such comments are misleading.
 
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  • #62
Dale said:
... Did you ever sit down and work out the conservation of momentum and energy as I recommended?

If so, then you should have seen that scattering can conserve both energy and momentum with just the electron, but absorption cannot. That is why a single electron can scatter a photon but cannot absorb it. It is all about conservation principles. The same conservation principles lead to both behaviors.
Yes, I sat down and did what you recommended so many times. I even explained (cited from Wikipedia) how the momentum is transferred to the rest of the atom ...

Yes, I understand that (and why) a single electron can scatter a photon, but tell me: the whole atom can? If not, why not? If yes, what decides if the atom as a whole or one of its electrons would scatter an incident photon?
 
  • #63
DanMP said:
the whole atom can?
Any charged particle can participate in elastic scattering. So as long as the atom is ionized it can participate. Inelastic scattering can involve even an unionized atom.

DanMP said:
If yes, what decides if the atom as a whole or one of its electrons would scatter an incident photon?
Whether or not the electron is bound or free. If the electron is free then the electron scatters, if the electron is bound then the atom scatters. A bound electron cannot be treated independently of the rest of the atom.

For loosely bound electrons and high energy photons the difference between the two is small. I.e. the scattering is elastic for free electrons and inelastic for bound photons, but the degree of inelasticity may be small. In such cases you may see some references blur the line.
 
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  • #64
Dale said:
... Whether or not the electron is bound or free. If the electron is free then the electron scatters, if the electron is bound then the atom scatters. A bound electron cannot be treated independently of the rest of the atom. ...
So, in scattering it is always about the electron ... We say that the atom scatters, just because the electron is part of an atom. This is very close to how I interpreted the absorption: the electron "receives" the photon but, because it is a part of an atom and momentum & energy are transferred to the rest of the atom, we say that the atom scatters/absorbs ...
 
  • #65
DanMP said:
So, in scattering it is always about the electron .
No, it is not always about the electron. It is only about the electron if the electron is unbound. I was pretty clear about that.

DanMP said:
the electron "receives" the photon
As far as I can tell the word “receives” has no meaning in this context.

At energies below pair production there are three basic interactions: a photon does not enter but does leave (emission), a photon enters but does not leave (absorbed), a photon enters and a photon leaves (scattering). “Receive” is not one of them.
 
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  • #66
Dale said:
No, it is not always about the electron ...
Ok, thanks for your replies.
 

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