1. The problem statement, all variables and given/known data Explain why the 1s2s (3P) excited state of helium is metastable? 2. Relevant equations Spin multiplicity = 2S+1 J = |L-S|, |L-S|+1,...,L+S, L+S-1,.. Selection Rules: ΔL = +/-1 Δm = 0,+/-1 Δs = 0 state must change parity Δj = 0,+/-1 j = 0 -> j' = 0 NOT ALLOWED 3. The attempt at a solution 2S+1 = 3 so S = 1 L = 0 J = |L-S| = 1 (only one value I think) How do I tell whether 1s2s (3P) excited state of helium is metastable? Note: (The 3 is superscript in front of P) Any help would be great, thanks!