Triplet and Singlet Helium States

[Jdraper]

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

 

[Quantum Defect]

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

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

 

[Jdraper]

Ok, thanks for clearing that up :)