Photon absorption -- What happens to the excess energy?

In summary: Stokes-Raman scattering is a relatively rare effect in which a photon of a certain frequency (in the visible and near-infrared range) imparts some of its energy to a free electron, and then continues as a lower-energy photon.
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TL;DR Summary
What happens to excess energy?
Wikipedia: "When a photon has about the right amount of energy to change the energy state of a system (usually an electron changing orbitals), the photon is absorbed."

What happens if a somewhat higher energy photon arrives?
 
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jeremyfiennes said:
Summary:: What happens to excess energy?

Wikipedia: "When a photon has about the right amount of energy to change the energy state of a system (usually an electron changing orbitals), the photon is absorbed."

What happens if a somewhat higher energy photon arrives?
It doesn't get absorbed unless your "somewhat higher" is within the range of Wikipedia's "about right".
 
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  • #3
Thanks. So it is reflected/refracted?
 
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It could be reflected or refracted or simply move merrily along as if the atom weren't there. It doesn't need to interact with every atom in encounters along its way.
 
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jeremyfiennes said:
So it is reflected/refracted?

You're mixing up models at different levels. Reflection/refraction are not things that happen to single photons. They are things that happen to light that is well described by the classical approximation of electromagnetic waves, which in "photon" terms means light made up of huge numbers of photons, not single photons.

If you're talking about a single photon, and it's not absorbed by an atom, the only other quantum level interaction that I'm aware of is Compton scattering.
 
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  • #6
Thanks. But if its energy is too high for it to be absorbed by displacing an electron into a higher orbit, but not high enough for Compton scattering, which was done using X-rays?
 
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jeremyfiennes said:
if its energy is too high for it to be absorbed by displacing an electron into a higher orbit, but not high enough for Compton scattering, which was done using X-rays?

If there is no interaction that can take place for a photon of that energy, what would you expect to happen?
 
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Disappear into the material and form heat, I suppose. Or maybe reappear at a reduced frequency in a low-level Compton scatter, which is presumably possible.
 
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I think my real doubt is whether an atom can extract from a higher energy photon what it needs to displace an electron into a higher orbit. And then re-emit the remainder as a lower frquency phton, analogous to a Compton scatter.
 
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jeremyfiennes said:
Disappear into the material and form heat, I suppose.

That would be an interaction, and the condition was "no interaction".

jeremyfiennes said:
Or maybe reappear at a reduced frequency in a low-level Compton scatter, which is presumably possible.

Same comment.

jeremyfiennes said:
I think my real doubt is whether an atom can extract from a higher energy photon what it needs to displace an electron into a higher orbit. And then re-emit the remainder as a lower frquency phton, analogous to a Compton scatter.

The answer to this is easy: no.
 
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Thanks. But this raises a further one: In Compton scattering a photon imparts some of its energy to a free electron, and then continues as a lower-energy photon. Is there any theoretical reason why it can't do this when displacing an orbiting electron from a lower to a higher state?
 
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jeremyfiennes said:
I think my real doubt is whether an atom can extract from a higher energy photon what it needs to displace an electron into a higher orbit. And then re-emit the remainder as a lower frquency phton, analogous to a Compton scatter.
https://en.wikipedia.org/wiki/Raman_scattering
 
  • #13
Thanks. It seems that Stokes-Raman scattering is what I am talking about, but that this is a relatively rare effect.
 
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