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Homework Help: Energy levels of helium atom

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data
    I have having difficulty explaining the splitting of helium atom energy levels for three different cases:
    1)Coulomb interaction is ignored
    2)Coulomb interaction is present but exchange interaction is neglected
    3)Coulomb and exchange interactions are present

    3. The attempt at a solution
    For 1) The helium atom has two outer electron. These electrons must have opposite spins due to pauli exclusion principle (-1/2 and +1/2). So we will have the case {n1=1 l=0} and {n2=1 l=0} for the first energy level. and {n1=1 l=0} {n2=2 l=0 or 1} for the second????

    For 2) Electron electron interaction is repulsive so it raises all energy levels wrt levels in 1). Coulomb potential is inversely proportional to separation of electrons.

    3)I know that triplet states are lower in energy than singlet states since in the triplet state electrons want to keep away from each other.

    I don't really understand these effects and where degeneracy in l is lifted and when it isn't. If someone could clarify this I would really appreciate it!
  2. jcsd
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