How can the technique of hitting electrons with photons be used to identify an unknown element?

Question

aaronq · Answer

It's based on the interaction of photons with electrons of atoms in question. When a photon striking an atom matches the energy of an allowed $\sf quantum~ state~ electronic~ transition$ absorption occurs. This interaction can be used to identify the elements (or ions) present because of how specific the energy match needs to be, so by subjecting a sample to different wavelengths, the resulting data (absorbance lines) can be compared to data base and find the element(s) present. This is technique is called "atomic absorption spectroscopy".