N2 Lowest-energy configuration First two excited configurations All shells fully occupied (N2): 1Sg+ (...) : Pg state (multiplicity, see later) (...) : is similar to hole  states are like those for , i.e. (see table)

spatial part spin part Two electrons are located in 2 different MO shells: both singlet and triplet states exist Two electrons are located in same MO shell and same spatial orbital: only singlet state 3. Two electrons are located in same MO shell but different spatial orbitals: e.g. O2, most stable configuration Symmetric spatial part L = l1+l2 = 0 Antisymmetric spin part = singlet  Antisym. spatial part Symmetric spin part = triplet 

S+ or S- ? f1

e.g.

Franck-Condon factor

e.g: ortho-H2 (I=1, Ns=3) para-H2 (I=0, Na=1)