Hi I am reading about transition in Helium, and I have come across a question. It is clear that triplet-singlet transition are not allowed, i.e. ΔS=0. But in my book (Foot's Atomic Physics) it says that Δl = ±1. This is what I don't understand. The selection rule Δl = ±1 we derived for Hydrogen, where there was no electrostatic interaction and only a single electron making the transition. In Helium we *do* have an electrostatic interaction and two electrons -- then how can we reuse Δl = ±1 again? Best, Niles.