One of the selections rules is that
for an electric dipole transition in a multi-electron atom, where J is the total angular momentum. Since
(as spin is not affected), the change in total orbital angular momentum is also 0 or ±1. Could someone give me a physical example how a zero change is possible? As far as I can understand, the change is ±1 for a single-electron atom and cannot be 0. The photon emitted carries the ±1 angular momentum away and hence angular momentum is conserved. We only consider 1 electron transitioning at a time, so I don't understand how the overall angular momentum change can be 0 then, if it can't be 0 for a single electron atom. I've been trying to look this up but the furthest I got was "this is just possible because of how angular momentum combines".
Could someone describe a real example to me how this works in practice?