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Neon energy levels in He-Ne laser

  1. Jan 16, 2015 #1
    Neon is the lasing element in He-Ne laser. The lasing transition(632.8nm) is from 3s to 2p. In the energy level diagram there is one 1.15μm transition from 2s to 2p. But we studied that 2s orbital have lower energy than 2p then how it is possible, in the energy diagram, 2s level have higher energy than 2p level and one transition of 2s to 2p?
  2. jcsd
  3. Jan 16, 2015 #2

    Quantum Defect

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    The notation in the diagram you reference is called Paschen notation. The labels are numberings of excited states, by energy. The "2S" does not refer to a "2s" hydrogen-like wave fundtion. Look at the reference given on the wikipage for a discussion of what nominal electron configurations correspond to the different Paschen notation labels.

    http://archive.today/pwve [Broken]

    Remember too that in multi-electron atoms, the kind of electron configurations that you learn to write as a beginning student (e.g. 1s^2 for He) are all approximations to the truth.
    Last edited by a moderator: May 7, 2017
  4. Jan 18, 2015 #3

    Thank you
    Last edited by a moderator: May 7, 2017
  5. Jan 19, 2015 #4

    Andy Resnick

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    Recall that Neon has more than 1 electron: the notation used in the level diagram is a not literally the same as for hydrogen:

    http://archive.today/pwve [Broken]

    As you can see, the 2P level corresponds to the outermost 3p electron, while the 2S state corresponds to the outermost 4s electron, which has a higher energy than the 3p electron.
    Last edited by a moderator: May 7, 2017
  6. Jan 19, 2015 #5
    Thank you, now it is in phase with what I learned!!!
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