What happens if a low energy photon collides with an atom in the ground state?

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Discussion Overview

The discussion centers on the interaction between low energy photons and atoms in their ground state, particularly focusing on what occurs when the energy of the photon is less than the energy gap between atomic energy levels. Participants explore concepts related to absorption, scattering, and the resulting thermal effects in the medium.

Discussion Character

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

Main Points Raised

  • One participant questions the outcome when a low energy photon collides with an atom in its ground state, suggesting that if the energy gap is greater than the photon's energy, the medium may absorb the light and convert it to heat.
  • Another participant proposes that the photon might pass through the atom without interaction, noting that scattering could occur, resulting in a change of direction and a slight gain in momentum for the atom.
  • A participant inquires about the warming of the medium when illuminated by light and seeks to understand the processes involved in light absorption.
  • It is suggested that certain atoms, molecules, or solids can absorb light, with some emitting light again while others convert energy to heat without radiation emission.
  • One participant reiterates the initial question about low energy photons and adds that infrared light is typically absorbed in molecular rotational or vibrational modes, which are lower energy, rather than atomic transitions.
  • There is a distinction made regarding the transparency of a medium to infrared light based on the presence of such molecular modes.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the interaction of low energy photons with atoms, with no consensus reached on the definitive outcomes of such interactions.

Contextual Notes

Participants discuss the dependence of absorption on the specific energy levels of atoms and the nature of the medium, highlighting the role of molecular modes in infrared absorption. The discussion does not resolve the complexities of these interactions.

Who May Find This Useful

This discussion may be of interest to individuals exploring photon-atom interactions, thermal effects of light absorption, and the behavior of different types of electromagnetic radiation in various media.

fxdung
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What happen if a small energy photon collide an atom in ground state that the gap between energy levels of atom is greater than energy of photon?It seems that the medium absorbs light and transform to heat?
 
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It might just pass through without interaction - the most likely case. Scattering is also possible: The photon changes its direction, the atom gains a tiny bit of momentum.

Visible light and most common gases are an example.
 
Why the medium become warmer when it is shined with light?What happen when it absorbs light?
 
Then some atoms, molecules, or solids there have transitions that can absorb the light. Sometimes they will emit light again, sometimes they lose their energy without emitting radiation (converting it to heat).
 
fxdung said:
What happen if a small energy photon collide an atom in ground state that the gap between energy levels of atom is greater than energy of photon?It seems that the medium absorbs light and transform to heat?
fxdung said:
Why the medium become warmer when it is shined with light?What happen when it absorbs light?
Usually most atomic transitions are in the visible range. So if you have a light with a slightly lower energy, then that means your light is in the infrared range.

Infrared light is typically not absorbed by atomic transitions, but rather it is absorbed in molecular rotational or vibrational modes, which are lower energy. If a medium has such modes then it will absorb infrared, otherwise it will be transparent to infrared.
 
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