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Let's take a black object for example. When waves of light (whether from the sun or a lamp) come into contact with the object, is it just the electrons (not the molecules) of the object that directly take in/contain the energy from the light source when the light waves comes in contact? Or, do the molecules also directly take in energy from the photons when the waves come into contact with the molecules?

Or, is it that the molecules just get their energy from the electrons that transfer the energy to them?

And when the object releases energy as heat, is it energy from the electrons, molecules, or both molecules and electrons that's being released?

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If you mean that the photon energy can be converted to excitation of the nuclear motion of the atoms that make up the molecule than the answer to the first part of your question is yes. Molecules rotate and vibrate at discrete energies and by absorption of a photon of the correct energy (typically in the infrared or millimeter to microwave range of the spectrum) these motions can be excited. We experience this as an increase of the object's temperature when we touch it. Of course the molecules can also be excited electronically.

Molecules that are excited electronically can loose their energy by sending out a photon (fluorescence or phosphoresence) or as heat by a process called intramolecular vibrational redistribution of energy (IVR), where the electronic energy is distributed over different vibrational motions of the molecule.

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  • $\begingroup$ So you're saying that both electrons and molecules will take in photon energy from waves that are impinging upon them and each will absorb photon. $\endgroup$ – adam3033 Aug 17 '15 at 16:55
  • $\begingroup$ And you're also saying that both the electrons and molecules can radiate photons? It's not just electrons that can emit photons? $\endgroup$ – adam3033 Aug 17 '15 at 16:56
  • $\begingroup$ If the molecule has a dipole moment you can imagine that the electric field of the light can couple to this dipole moment and that it oscillates with the frequency of the light. When the frequency corresponds to one of the vibrational or rotational energies of the molecule it will excite this motion. The opposite is also true, if you look at the ammonia maser for instance, where NH$_3$ molecules are prepared in an excited level (of the inversion state, so associated with motin of the atoms) these molecules release their energy by emitting a ~24GHz photon. $\endgroup$ – Paul Aug 18 '15 at 7:18
  • $\begingroup$ Thanks for that very helpful answer. I should also ask, when it comes to reflection of light from any object, is it the electrons, themselves, that are releasing energy and re-emiting photons, the molecules (Raman active), or sometimes both? $\endgroup$ – adam3033 Aug 19 '15 at 6:40

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