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Triplet and Singlet Helium States

  1. Jan 13, 2015 #1
    I have a theoretical question, I just recently learned that the spin triplet S=1 of helium in the state 1s2s is lower in energy than the 1s2 state due to the exchange interaction. I then learned that this 1s2s state has a shorter lifetime than the 1s2 state, can anyone explain why this occurs?

    Thanks, John
  2. jcsd
  3. Jan 13, 2015 #2

    Quantum Defect

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    This is not correct. The 1s^2 state (1^S_0) is the ground electronic state. The 1s2s state can be a singlet (2 1^S) or a triplet (2 3^S), depending upon whether the spins are parallel or antiparallel. The 1s2s triplet state and the 1s2s singlet state will be long-lived because they do not have strong (one-photon, electric dipole allowed) transisitons to the ground state.

    c.f. http://scholar.uwindsor.ca/cgi/viewcontent.cgi?article=1060&context=physicspub has some discussion of excited He-like atoms
  4. Jan 13, 2015 #3
    Ok, thanks for clearing that up :)
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