GOT IT. EVEN THINKING ABOUT A CRAZY HYPOTHETICAL SITUATION: IMAGINE AN ATOM IN WHICH WHO WOULD BE ATTACHED TO THE NUCLEUS WOULD BE THE ELECTRON AND WHO WOULD BE ORBITING ARE THE PROTONS. COULD ALL PHENOMENA OF CHANGING ORBITS THROUGH GAIN OR LOSS OF ENERGY, OR EVEN THE "ELECTRIC" PHOTO EFFECT...
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About changing permitted to prohibited bands. The valence and conduction bands. What I really wanted to know was whether the proton could play the role of the electron in that sense. If it would be possible.
What would happen if the protons started to have orbital movements with energy gain and loss, changing orbital bands, at the same time as the electrons?