Hello, there is one thing about atomic states I don't understand. I try to look at what states are possible for a np^2 configuration (that is, all lower shells are filled and don't contribute to the case). For example my textbook says that the [tex]~^1 P[/tex] state is not allowed because of the Pauli principle. But now, let's have a look at what [tex]^1 ~P[/tex] means: L = 1 S = 0 The spins are clearly anti-parallel. For L = 1 we have M_L = -1,0,1. I don't see any problem finding m_l's adding up to those M_L's without breaking the Pauli principle. So what am I not getting?