I pretty much understand the idea of photon of some wavelength λ exciting an electron in atom above the ground state if the difference between the ground state and a higher energy level is exactly hc/λ. Not hard, but what happens to the electron and the atom when the photon energy is below the excitation energy? From what I've been reading in Optics by Hecht it seems that the photon will pass through the electron cloud and its electromagnetic nature will set the electron cloud into an oscillatory motion making it so the atom now behaves like an oscillating dipole (similar to those in radio towers). This oscillating dipole will then emit a photon of the same frequency as its oscillation (or the same frequency as the passing photon, or maybe coincidentally both, I'm not sure). What happens to the original photon however? Does it just continue to move on, gets weakened and moves on, or does it get absorbed by the cloud when it sets it into an oscillatory motion? I suppose conservation of energy would point to either the second or third option no? Also, what happens when the photon is not carrying precisely the excitation energy, but more? Will the electron get promoted above ground level and then the atom absorbs the rest of the energy as just kinetic? All right, thats about it. Thanks in advance guys.