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Specific absorption/ emission

  1. Jul 21, 2011 #1


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    This is my understanding; please, correct me if I'm wrong.
    If you bombard an atom with em-waves they will never break loose electrons until a certain threshold frequency. At this point the intensity of the light (or the amount of photons) striking the atom is proportional to the number of electrons ejected. The additional energy in the photon, beyond the energy required to break the bond, goes into kinetic energy of the electron. Electrons also absorb and emit specific frequencies of light when jumping between specific orbitals.
    Does the threshold frequency only apply to breaking an electron loose, i.e. out of the atoms orbitals, and does this mean they can absorb any frequency above the threshold? Do the emission/ absorption frequencies only happen at discrete, exact values (versus a distribution of values)? Can they absorb higher energy photons, jump orbitals, then take the remaining energy as kinetic or even re-emit it as a lower frequency photon?
  2. jcsd
  3. Jul 21, 2011 #2
    I am not an expert, but I will take a shot at answering your questions.

    Yes. Only bound particles are restricted to carrying specific amounts of energy.

    No. The uncertainty principle dictates that a process with a known amount of time has an uncertain amount of energy. Spectral lines are not infinitely thin. Instead, there is a very small range in which the energy can be absorbed/emitted.

    If the electron is still bound, no. The energy of a photon emitted or absorbed can only be equal to the difference between two energy levels in the atom.

    It actually took me some research to find these answers, so I hope you like them.
  4. Jul 22, 2011 #3


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    Nice, thank you very much. That all makes a lot of sense.
  5. Jul 22, 2011 #4
    You're welcome. I guess I should also add that, while the electron can't absorb a fractional amount of energy from a photon, the atom as a whole can, since the atom itself is not bound.

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