The discussion centers on the energy levels and lifetimes of helium states, specifically the spin triplet state (S=1) of helium in the 1s2s configuration compared to the 1s2 state. It is established that the 1s2 state is the ground electronic state, while the 1s2s state can exist as either a singlet or triplet. The 1s2s triplet and singlet states are characterized by their long lifetimes due to the absence of strong electric dipole allowed transitions to the ground state, contrary to the initial assumption regarding their lifetimes.
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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.Jdraper said: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