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

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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.
 
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Why the medium become warmer when it is shined with light?What happen when it absorbs light?
 
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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).
 
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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?
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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