Can someone explain to me how an atom can absorb the energy of an incident photon without being ionised? What is the photon energy transformed into and how is it transferred between the photon and the atom (what part of the atom absorbs the energy?). I can't find anything helpful online - the resources I've managed to find are either too simplistic or far too complex. I'm hoping that this can be explained without a quantum mechanical treatment? I appreciate any help.