# Partial absortion of a photon

In atoms, there are electronic energy levels, when there is a match between those and a light photon energy, an electronic transition ocurs.

Example and question

Suppose an atom has a levels $$0$$, $$1$$ and $$2$$ with $$E_2>E_1$$ (relative to $$E_0$$). Then if a photon comes with energy $$E_2>E_{\mathrm{ph}}>E_1$$ why can't it be partially absorbed? So the electron moves to $$E_1$$ and the extra energy of the photon is released. Is it possible?

• If the photon energy is below the threshold for exciting the atom, the photon still can scatter from atom elastically, but the absorbed energy-momentum by atom as a whole is normally too small to be noticed in the final photon. – Vladimir Kalitvianski May 30 '18 at 6:40
• In case of non resonant photon an inelastic interaction is also possible; it is just much less likely than the elastic interaction. It is called Raman scattering. – Vladimir Kalitvianski May 30 '18 at 6:47
• @VladimirKalitvianski So we have three phenomena. Elastic scattering non elastic scattering and absortion. But why we see only absortion lines on atomic spectra? Can't a photon with higher energy than the first transition be partially absorbed? – santimirandarp May 30 '18 at 6:54
• Yes, it can. Read a Wikipedia entry for Raman scattering, please. – Vladimir Kalitvianski May 30 '18 at 6:55