Bonding and Antibonding Molecular Orbitals

internuclear distance R

3

The lowest-energy bonding and antibonding molecular orbitals (MO) for a homonuclear diatomic molecule are shown, as the internuclear distance

R

is varied. These MOs are designated 1

σ

g

(or

1sσ

) and 1

σ

u

(or

1s

*

σ

), respectively. The red contours designate negative values of the wavefunction. In the separated atom limit (large

R

), the MOs approach a pair of noninteracting 1s atomic orbitals. In the united atom limit (

R=0

), the 1

σ

g

and 1

σ

u

collapse to 1s and 2

p

z

atomic orbitals, respectively. At the equilibrium internuclear distance, the minimum of the energy curve, the bonding orbital is optimally effective.

The contour curves take a few seconds to smooth out as you change

R

. Only qualitatively representative results are intended.

Snapshot 1: equilibrium internuclear distance

Snapshot 2: separated atoms

Snapshot 3: united atoms

S. M. Blinder