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A question for helium energy transition

  1. Apr 27, 2015 #1
    For S=0 parahelium, 1s2p-1s2s transition is allowed, but why there is no transition between 1s3p-1s3s? I think the only difference for the electron configurations is principal quantum number. The selection rules applying for 1s2p-1s2s can also be applied to 1s3p-1s3s. In other words, there is no selection rule to forbid the 1s3p-1s3s transition.

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  2. jcsd
  3. Apr 27, 2015 #2

    Quantum Defect

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    I think that it should be allowed. The chart is showing observed lines. What wavelength/frequency would the 1s3p-1s3s transition be? It may be that the chart is showing prominenet lines in a particular wavelength region. The one you are looking for might lie outside of this window.

    This website shows the transition on there energy level diagram: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/helium.html
  4. Apr 27, 2015 #3
    Thanks for your reply. Your idea currently is only reasonable explanation for the missing transition though I still expect more details. BTW, graph in the link clearly shows no transition between 1s3p-1s3s.
  5. Apr 27, 2015 #4

    Quantum Defect

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    Whoops. You are correct, I mistook the 3p-2s for the one you were asking about.

    Here is a better source: http://www.nist.gov/srd/upload/jpcrd382009565p.pdf
    This source lists the transition (#73 in the list for He, on page 618) as being 1,344 cm^-1 -- in the infrared region.
  6. Apr 27, 2015 #5
    Thanks so much for the excellent reference! I will read it carefully.
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