Does molecular vibrational transition and consequent emission of infrared radiation involve electrons changing energy level? In wikipedia, about vibronic transitions it says "Most processes leading to the absorption and emission of visible light, are due to vibronic transitions. This may be contrasted to pure electronic transitions which occur in atoms and lead to sharp monochromatic lines (e.g. in a sodium vapor lamp) or pure vibrational transitions which only absorb or emit infrared light.". Does this mean infrared radiation is emitted without electrons playing a direct part? What about changing in molecular rotational energies? Also, I understand reflection is not a radiation absorption-emission phenomena, so can you explain what actually happens to the photons? Same thing for radiation scattering.