Hydrogen molecule antibonding orbital

To get the molecular orbital of the hydrogen molecule, the orbital equations of the two atoms are combined. When the orbital equations are added together, the result is a bonding molecular orbital that extends over both atoms. Subtracting the orbital equations of the atoms produces an antibonding molecular orbital. This process is called the linear combination of atomic orbitals or LCAO. 

The first excited state in the hydrogen molecule is an antibonding orbital. 

When the H3P-Ni-PH3 angle becomes 90°, hybridization between the dxz and s atomic orbitals, rather than s-p hybridization, results in directed orbitals suitable for coordination with the PH3 ligands. In the process, empty antibonding orbitals having an s and dxz nature are created, as sketched in Fig. 4.16. Their orientation and symmetry are suitable for interaction with the hydrogen molecule. Now the... 

The two electrons in the hydrogen molecule will occupy the lower energy bonding orbital, and none will go into the antibonding orbital. 

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