Equivalence of the molecular orbital and valence bond models

3 Equivalence of the molecular orbital and valence bond models 

This is also a spin singlet state. Furthermore, this is a repulsive state i.e., it is not a bound state. 

For the excited configuration 7 aj 1, there are two states, one singlet and one triplet. This situation is similar to that found in the excited configuration ls12s1 of the helium atom. The singlet and triplet wavefunctions for these excited configurations are  

On the other hand, the (un-normalized) ground and excited (if-) state valence bond wavefunctions are 

Wavefunction Vq refers to the situation where both electrons are on nucleus a or nucleus b, i.e., ionic structures. Now it is obvious that the valence bond wavefunction //+ considers only covalent structure, while the molecular orbital wavefunction t has an equal mixture of covalent and ionic contributions. Similarly, expanding the wavefunction in eq. (3.2.27) yields 

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