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Tuesday, April 5, 2016

Hydrogen Atom Emission and Absorption of Photons


The description we often read is of an electron emitting or absorbing a photon and thus moving to a higher or lower orbit. Just how can an electron do this? Is the electron full of photons?
The answer must be more realistic than that. Using the Bohr model of the atom we note that the electron has some speed which determines its orbit and there is some interaction with the positively charged proton via photons that prevents the electron from escaping.
For planets around a sun or moons around a planet, the speed and therefore momentum and kinetic energy increases as the orbital radius decreases. If the mass and therefore momentum increases for a given speed then the orbital radius increases. If the mass of the object around which the satellite is orbiting increases then to remain at the same orbital radius the orbiting object must increase speed or lose mass.
But in the case of the electron, an increase in energy means an increase in orbital distance. Does this mean the speed increases? If orbital speed of the electron was increased on its own then the electron would simply escape the atom altogether.
It seems to me that the most logical way to model this condition is to consider the electrostatic force binding the electron to the proton and the speed of the electron (kinetic energy) to change in sync, that is, together.
Consider the emission of a photon from the atom. It is usually said that the electron emits this energy on its own but it makes more sense to me that the electrical part of the photon is emitted from the force binding the electron to the nucleus and the magnetic component is transformed from the momentum of the electron. Together we have both less speed and less binding force (the negative electron to the positive proton), the two components combining to make up the emitted photon or a photon that is absorbed divides into more speed for the electron and more binding energy between the electron and proton.
Thus we have two forms of energy combining to form the emitted photon, the energy of the electron and the energy of the field between electron and proton, both of which contribute to a photon.
I note that a free electron can be kicked along by a photon (can interact with a photon) but does not absorb any photons. It seems clear that absorption requires special conditions, such as is present in the hydrogen atom, and that the electron, when part of an atom, can no more absorb or emit a photon than a free electron can ~ it requires both parts of the EM wave (Electric and Magnetic) to be absorbed simultaneously and symmetrically.