I was wondering how much kinetic energy needs to occur in atom until it emits a photon. For example if you accelerate an atom (like LINAC) what energy and speed is needed for it to emit energy? Or if you heat/vibrate up a copper plate and it starts to glow, what kinetic energy is needed for the emission to start occurring? My reasoning on it: I assume that the point at which the atom can emit a photon is at the point where the atoms electron that is the farthest away from the nucleus can become excited to a higher state creating an excited electron and hole. At which time it will decay/de-excite and emit a photon. Before this threshold the atom will just hold the kinetic energy (vibration, rotation, translational)? Given that kinetic energy can be given to the atom in variable amounts (not quantified, quanta)? If you accelerate an atom below the point of exciting its electrons then no energy will be emitted (photons). This being true then if kinetic energy is added beyond the threshold of exciting the farthest out electron, then the kinetic energy will become quantified and will excite the atom where a hole and excited atom will be created and a fixed photon will be emitted. So for example if you accelerate a hydrogen atom before the ionization energy then the atom will stay kinetic, but if you excite to 1312.0 kJ/mol then it will ionize and then with recombination emit a photon. Is this right? Any sources would be great.