In an introduction I read the following sentences:
"In excited singlet states, the electron in the excited orbital is paired (by opposite spin) to the second electron in the ground-state orbital. Consequently, return to the ground state is spin allowed and occurs rapidly by emission of a photon."
I'm not really sure if I understand this correctly. What does "spin allowed" mean?.
Normally, the selection rules are $\Delta m=\pm 1$. If the electron just decays to the ground state, this shouldn't depend on the state of the second electron in the ground state, does it? Do the selection rules change if the whole Atom is in a singlet state?Btw when the Atom is excited, the Atom isn't in a singlet state anymore?