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I understand that electrons cannot join already filled orbitals. I also understand that in case there's a hole in a lower orbit [1], an electron can emit a photon and change its orbit (e.g., L->K).

What is the physics that prevents an electron from emitting that same photon but keeping its orbit when there's no lower orbit with a hole? I.e. what kind of physics prevents an electron from losing energy within the same orbital? Is it just the lack of trigger for that to happen?

My naive assumption would be that since an electron can emit a photon then there's a probability that that could happen at any time. And since the electron would have nowhere else to go, it would stay at the same orbital.

[1] I'm ignoring spins for simplicity.

V13
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    Conservation on energy. An orbital (as the term is usually used) has a fixed energy. – Sebastian Riese Mar 12 '23 at 01:48
  • That would apply if there was energy being created from nothing. But tin this case the electron is emitting a photon and the orbital doesn't have energy by itself (i.e., there's no energy there when there's no electron). The electron emitting a photon wouldn't result in any loss or gain of energy in the system. So the question in a sense is: what's the physics that forces an electron in an orbital to have no less than a certain energy? – V13 Mar 12 '23 at 03:16
  • Is your question, whether an atom can coherently emit a photon in a collision, without changing it's state? (Your comment seems to imply, that you consider the atom plus something as system, so that the emitted photon does not violate conservation of energy. – If so, please clarify your question.) – Sebastian Riese Mar 12 '23 at 10:40
  • Related Question: https://physics.stackexchange.com/questions/20635/is-photon-emission-possible-without-electrons-changing-energy-levels – Sebastian Riese Mar 12 '23 at 10:42
  • Thanks. I think that that is a bit different. I'm looking at this: https://youtu.be/es6f90JcJ2k?t=1240 (at 20:40), where the (3) electron changes state, emitting an x-ray because of the lower energy level of the K shell. I'm trying to understand what is the physics that prevents that electron from emitting the x-ray before the (2) electron gets ejected by the gamma ray. – V13 Mar 12 '23 at 14:54
  • It can't emit it before, but coherently at the same time (just as a high energy photon can cause coherent two electron photoemission) – however, such processes are typically supressed compared to the single-particle emissions followed by other processes (unless the single particle process is forbidden in first order, e.g. due to symmetries). In the language of Feynman diagrams this becomes clear – the multi-partcile process has more vertices, so more powers of the (small) coupling constant $\alpha$. – Sebastian Riese Mar 13 '23 at 21:53
  • (If you edit in those details into the question, ideally paraphrasing the process discussed in the video, your question will become a very good fit for this site, and have a good chance of gaining upvotes.) – Sebastian Riese Mar 13 '23 at 21:54

2 Answers2

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An orbital is a legacy name for the state of a given electron within an atom from times when we thought that electrons orbit a nucleus like planets orbit the sun. Photons are emitted by electrons changing their internal state, or as one could say: changing their orbitals. Each orbital is directly related to the electron's energy, so when that energy is changing, then an orbital also has to change. But once again, what is really changing is the state of the electron and the idea of orbitals is just a useful analogy.

Noct
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  • So is it the exclusion principle then that prevents an electron from changing its state because there's another electron with that state? – V13 Mar 12 '23 at 14:57
  • @V13 If I understand you correctly, then yes. Because of the exclusion principle you cannot have two electrons with the same state within an atom. So an electron on a higher orbital cannot 'drop' if the lower orbital is already occupied. – Noct Mar 12 '23 at 15:28
  • Are "orbital" and "electron state" the exact same thing? If yes, then I believe that this answers the question. Otherwise the question is practically about what is the physics that ties the orbital with the electron state. – V13 Mar 12 '23 at 18:06
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    @V13 Yes, they are. As I mentioned at the beginning of my answer, an orbital is an old name. – Noct Mar 12 '23 at 19:47
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To conserve energy it emits a photon In an excited state the electron is not much stable to achieve a more stable state i.e more negative energy the electron jumps to a lower orbital.since the energy of electron should remain conserved by achieving more -ve energy it emits a photon of positive energy (photons always have +ve energy).It specifically emits a photon since electrons interact electromagnetically.It is possible for an electron to emit photon as long as it is excited state.

Now what prevents an electron from emitting a photon is that it does not lose its energy in certain configurations of angular momentum and velocity and radius.In that special numbers allowed for an electron in the atom of angular momentum.The electron resonates and it is what the resonance probability that you call as manefistation of an electron that is an orbital

Maanik Khurana
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  • That is what's happening, yes. But (using your words) what is the fundamental physics that prevents an electron from emitting a photon when it isn't in an excited state? Or otherwise, what is the fundamental physics that prevents the electron from "losing energy in certain configurations of angular momentum and velocity and radius"? – V13 Mar 12 '23 at 18:11
  • The fundamental physics says that electron should emit a photon when it comes to a lower energy state.If you say on basis of rutherford model the electron maybe within accelrated motion,but the frame of refernce is non-inertial so the maxwell equation does not work here.And within the atom the wave packet of electron is stationary since its a standing wave.So electron does not moves at all – Maanik Khurana Mar 13 '23 at 11:09