# What causes the triplet state in Helium?

I am not familiar with the notation used on wikipedia (http://en.wikipedia.org/wiki/Triplet_state). Is there a more physcial way to explain the cause of the triplet state (maybe without referencing the wave function)?

In my book it says the folllowing:

'For the overall spin of the electrons exist the possibilities S = 0 and S = 1, which is >why the term scheme of the Helium atom splits in a singulet and a triplet system.'

I also found that J (total angular momentum quantum number) = L+-S can be 0,1 and 2 but I can't see why.

On a related note: does the intercombination prohibition mean that one helium atom can only be singulet or triplet forever?

Edit1: Thanks for your quick answer. But aren't you implying in your solution that L=0 (due to L-S <= J <= L+S)?

• The $1s$ triplet to singlet transition is forbidden but it will occur - just rather slowly. Also the transition is only forbidden for emission of a photon. The triplet state can decay in collisions with other atoms, or in the liquid or solid by transferring energy to the lattice. – John Rennie Jun 24 '14 at 11:45

• I think this is not fully correct: the singlet state is the antisymmetric spin state, $|\uparrow\downarrow\rangle - |\downarrow\uparrow\rangle$ (up to a constant), whereas the complement in spin space is three dimensional and consists of symmetric states, including those in which the spins are parallel, but also $|\uparrow\downarrow\rangle + |\downarrow\uparrow\rangle$ – doetoe Jan 11 '15 at 15:30